PGRs and Medical Marijuana


Disclaimer: The following material is written in the interests of education and harm reduction.

Since exposing PGR containing products in 2010 – 2011, I have been informed by the California based Werc Shop (medical marijuana testing laboratory) that 15% of medical marijuana they test fails the ‘pesticide’ screen, of which roughly 50% is paclobutrazol. See lab results following (with thanks to the good people of The Werc Shop).




All I can really say about this more than sad situation is that it is a disgrace that medical marijuana patients are being unnecessarily exposed to potentially, harmful to human health, toxins because of unethical growing practices on the part of too many.


What it now needs to come down to is that medical dispensaries should be testing the produce they sell for paclobutrazol and other chemical plant growth regulators (PGRs). Either this or, as with other U.S. medical States, California should regulate in such a way where the medicine supplied by dispensaries is grown to ethical standards. What this means is take the growing out of the hands of cowboys and let the professionals handle it based on criteria/legislation that protects medical users.  Sorry people, but when “medicine” (I stress “medicine”) is loaded in harmful to human health toxins it simply isn’t medicine. Let’s not BS ourselves.


Plant Growth Regulators (PGRs)




(E.g. Superbud, Phosphoload, Boonta Bud, Rox, Rock Juice, Flower Dragon, Gravity, Bushmaster, Cyco Flower, Yield Masta, Mr No, Yellow Bottle Ooze Bloom etc)


This article isn’t so much about ideal growing practices but, instead, a warning about less than ideal growing practices amongst cannabis cultivators.


That is, the use of non-compliant and potentially harmful chemical PGR (Plant Growth Regulator) products used during flowerset by far too many growers.


Just some of these products are Superbud (Australia), Phosphoload (Superbud rebranded, North America), Rock Juice (Australia), Flower Dragon (North America), Gravity (North America), Bushmaster (North America), Boonta Bud (UK), Rox (UK), Cyco Flower (Australia), Mega Bud (North America), Dr Nodes (renamed Mr No – North America), and Yield Masta/Sudden Impact (Australia and NZ).


In all cases the aforementioned products contain chemical PGR actives (subclass “Growth Retardant”) such as paclobutrazol (PBZ), chlormequat chloride (CC), and/or daminozide.


These chemical actives:


  1. Are classed as systemic pesticides
  2. Are scheduled poisons
  3. Have long withholding periods
  4. Are in many cases and most countries banned for use on food/consumable crops
  5. Are subject to strict regulations, pertaining to registration and use (crop type, application rates and times)
  6. Are, in the case of daminozide, rated as a “probable human carcinogen” and in the case of paclobutrazol rated with, “This substance/agent has not undergone a complete evaluation and determination under US EPA’s IRIS program for evidence of human carcinogenic potential”. Additionally, paclobutrazol has been shown in studies to be toxic to the liver.
  7. Are, in many cases, sold illegally through the hydroponics retail sector and falsely marketed as containing organic components.




In early 2010 I published “The Curious Case of the Flower Dragon”.  In this piece I spoke about Flower Dragon – a bloom additive that is/was being sold through the hydroponics industry in the UK, Europe and North America with claims of being a “phytomineral” based flowering supplement, containing “citrates”, “tartarates”, “phosphates”, “arginates”, and “rare earth elements”. At that time I outlined that based on the products labeling, its registration with the Oregon and Californian Agricultural Departments, and dubious marketing, Flower Dragon was, in all probability, a PGR based flowering additive.


In May of 2011 information surfaced that Flower Dragon, Phosphoload, Top Load, Bushmaster and Gravity had been “quarantined” and removed from the Californian and Oregon markets following an investigation by CDFA (Californian Department of Food and Agriculture) which discovered noncompliant PGRs in Flower Dragon and several other products.


During the investigation, Flower Dragon was found to contain paclobutrazol and daminozide  (Alar), the latter being a PGR that was once used widely in the US apple industry before being banned for use in any consumable crop in 1989. Top Load was found to contain daminozide (Alar), while Phosphoload, as with Flower Dragon, was found to contain both paclobutrazol and daminozide. The fact that both Flower Dragon and Phosphoload contained almost identical actives was no surprise – both have their origins with South Australian based company Dutch Master (DM). Dutch Master Phosphoload (albeit registered behind a front company, Nuegn Garden Exports, PO Box 12271, Melbourne, Victoria, Australia) was likely developed by onetime DM employee Steve Berlow, who had gone out on his own, starting Envy Plant Products (BC) and releasing Flower Dragon, or as the case may be, rebranded Dutch Master Phosphoload plus red dye. Since then Yellow Bottle Ooze Bloom has also been busted – it was found to contain daminozide/Alar by the CDFA after lab testing. I will post FOIA data on lab tests and other when I am able to access it.


In the case of ‘Bushmaster’ and ‘Gravity’, both products were found to contain paclobutrazol – a potential toxin (chemical PGR) with links to causing liver disease.


LAB RESULTS – Tests Conducted on PGR Containing Products in March, 2011 (FOIA Data obtained from Californian Department of Food and Agriculture)

Flower Dragon: 18,400-18,650ppm daminozide, 30-46.3ppm paclobutrazol
Phosphoload: 17,800ppm daminozide, 20.6ppm paclobutrazol
TopLoad: 3,467ppm daminozide
Bushmaster: 271ppm paclobutrazol
Gravity: 516ppm paclobutrazol

Download CDFA lab analysis and recall notices of the aforementioned products (1.8meg PDF)


Deceptive Marketing of PGR Based Products

PGR containing products are typically promoted as organic and safe. This creates confusion amongst the cannabis culture as to the implications of using these – stated to be – organic products.

For example, Humboldt Countys Own Bushmaster (paclobutrazol) is sold listing “Active Ingredient: 1.5% Ascophyllum Nodosum (Sea Kelp).

And Gravity (paclobutrazol) is marketed with this,


“Our uniquely prepared kelp extract and phosphorus based additive will harden your flowers from the top to the bottom. A little goes a long way. Use once or twice about 3 weeks before the end of a plant’s cycle. Adds size and weight to flowering plants.”

[End Quote]

As for Flower Dragon (paclobutrazol and daminozide),


“… This highly specialized mixture of selected rare earth elements and phyto nutrients supports your newly supplied bio available phosphorous by helping focus your plants internal energies into flowering, producing large abundant flowers, without the necessary lag…… a process commonly known as “Speed Shifting”. To do this Flower Dragons harnesses the amazing natural power of Arginates and Rare Earth Elements (REE’s). These unique phyto nutrients synergistically work with our micronutrients to allow your plants their most naturally rapid transition into flowering”

[End Quote]

And Dutch Master Phosphoload (paclobutrazol and daminozide)


“Dutch Master PhosphoLoad utilizes a new technology which extracts unique isolates from coal derived humates. These are powerful earth elements that unlock the floodgates for a fast & powerful flowering response. When used, PhosphoLoad produces dramatically larger and heavier yields of flowers with an average yield increase of 25 to 30%. “

[End Quote]

While the onetime Dutch Master Superbud (paclobutrazol and daminozide) was marketed with,


“SUPERBUD is the most innovative & powerful flowering additive to hit the market EVER!

SUPERBUD utilizes a new technology which extracts unique isolates from coal derived humates. These Humatic Isolates are powerful rare earth elements that, when combined with Dutchmasters propriety Phospholipid Technology, unlocks the floodgates for a fast & powerful flowering response.

The unique combination of elements helps your plants finish the growing cycle extremely quickly without the usual lag period that occurs when you turn your light cycle down to initiate flowering.

The Phospholipid Technology (first incorporated in Dutch Master Folitech) then increases or switches the flowering receptor sites on, which then allows these Humatic isolates to exert their powerful flowering effect.

Plants flowered with SUPERBUD stop their upward growth almost immediately & start to form numerous, tight and heavy clusters of flowers that continue for many weeks.

Growers who use SUPERBUD report larger heavier yields of flowers with an average yield increase of 25 to 30%. “

 [End Quote]

One of the greatest promoters of Superbud, prior to its recall in 2003, was a moderator, Feral (now deceased – RIP), from the now defunct medical marijuana forum Natures High ( Feral, a larger than life character, had been promoting Superbud to Natures High members for some time, mirroring Dutch Master’s claims that Superbud was a 100% organic and safe product. In 2003, when it became apparent that Superbud was anything but organic, Feral became the most ardent attacker of Superbud during the internet campaign against it. By this time he had undoubtedly convinced many of the other members of Natures High (and others) to use Superbud, leading med growers to believe (in line with Superbud’s marketing) that Superbud was organic. This aside….

His first post in the campaign against Superbud read:


“from the day of it’s release, the makers of superbud, dutchmaster, claim no harmful ingredients are used in its manufacture. today i find out that sb uses a pesticide used in the hydroponic lettuce. industry, untill being banned as it contains

have we been had?????? independent analysis says yes.

the inventor looked tm in the eye and stated that there was definatley no harm full additives. holy shit, they lied by the looks of it.

steven carruthers, owner of the publication “hydroponics aust” found out and stands to loose alot of advertising revenue blowing their cover. he feels it his duty to the public to make info(as my duty to tell yous). dutchmaster spend big dollars with him, not for long by the looks of it. good on him. the hydro industry is well pissed off here as they pride themselves on a pesticide free grows. this WILL smear the industry.

this is hot off the press.

PLEASE DON’T PANIC!!! i have stopped using it today though.
the full report of this product will be available to me next week.
sorry, please don’t shoot the messenger!!!!!!

if this is rite i am going to call for a ban on dutchmaster products for missleading us.” Posting dated 16/10/2003

[End Quote]

The rest is now history in what became the biggest shitfight on cannabis forums ever . Legends were made, myths found their origins, reputations were ruined, and Dutch Master’s Superbud Juggernaut was given a dose of Kryptonite (well, not quite – Phosphoload was available within weeks).

I was recently forwarded an email from a European distributor of Flower Dragon and asked to comment. The email had initially been sent to the European distributor by Steve Berlow of Envy Plant Products/Flower Dragon responding to concerns that the distributor had concerning Flower Dragon containing unlisted and potentially harmful actives.

The email read,


“Re: Flower Dragon

(name edited)

I think to better explain Flower Dragon and what it is and to allay some misconceptions we really need to look first at what Paclobutrazol is and what it isn’t so you can be better informed.

Firstly Paclobutrazol is a safe product to use and is used on many crops worldwide including; Avocadoes, Peaches, Cherries, and Mangoes – in fact it is more safe than many of the chemical salts used to make regular nutrients for the plants. People who say that Paclobutrazol is unsafe or unhealthy to use are misinformed and should look to correct scientific data and not the growers forums for their information – LOL!

The LD50 or the amount needed to give rats to cause death in 50% of them is 5, of weight. For a human this would equal 378,000mg or almost ½ a kilogram for an average person! Compare this to the LD 50 of say Potassium Nitrate, a commonly used salt in every hydroponic fertilizer of 3,500mg/kg.

This mean that potassium nitrate is 50% more poisonous or deadly than Paclobutrazol!!! But of course we know that Potassium Nitrate is not poisonous or dangerous to us in normal amounts – so it is easy to see how ridiculous these health scares for paclobutrazol is.

So now for Paclobutrazol and growing of resinous plants.

Paclobutrazol is a very poor choice for providing the plants as it severs (disconnect ) the pathway responsible for producing the resins – the gibberilic pathway.

The gibberilic pathway is also responsible for the upward growth of the plant. So paclobutrazol is good for controlling the height but not for resin plants as it stops the production of resin also!

An easy way to see for the use of paclobutrazol is to see that the plant does not produce very much resin at all!
So we can see this is maybe a good choice for the height control but not if the plant you want to grow also makes resins. So now that we know a little of the background of Paclobutrazol let us look at Flower Dragon.

Flower Dragon was never designed as a height control product. It was designed as a product that can make the flowers much larger with more resins – that are of high quality. The fact that Flower Dragon can control the height is a secondary benefit but not the main features or why Flower Dragon was design. The simple fact that Flower Dragon makes the plants produce much resin demonstrate that Flower Dragon is not a paclobutrazol based product.

Flower Dragon uses a different method to make the flowers larger and the plant produce more resins. For this we need to make the gene expression. The gene expression control how plants ( and animals and people ) can grow and develop in certain ways. For this we need to make the target genes produce more peptides and other compounds – such as sterols ( up-regulate ) that make for resin increases and to make other target genes make less compounds ( down-regulate ) to allow the flowers to be larger. This regulation occurs within the Shikimic Pathway ( which also regulate the production of gibberlinins ). By allowing for both up and down regulation of the genetic expression we can produce the results which are desired to us ( bigger flowers with more resin ). The part that gibberilin play in this is that for the flowers to develop fully – the production of gibberilin should slow – but not completely stop- this is important as gibberilins are also important in the production of resins and for the expansion of the cell membranes – but too much gibberilin make the flowers not grow as we would like.

The important compounds that Flower Dragon uses is 2 proprietary compounds develop by us.

One is what is generally known as an Arginine ligated triazole compound. The specific type and structure of this compound is of course a trade secret to us and so unfortunately Tomas we cannot disclose the precise nature of this compound – for it would then be easy for others to copy. The other is what is known as a quinalone type compound. Of course once again the exact type is also a trade secret to us. It maybe be a business mistake for me to disclose even this much of the secret and make it easier for others to copy but I know you have customers who would like some answers. I can assure you that both of the compounds are quite safe – in fact I regularly consume product that has been grown with Flower Dragon. I do this with pride!

The other ingredients are there to support phosphorus mobility and metabolisn. These include Citrates and Tartarates.
Citrates and tartarates are carboxylate anions that assist the plant in mobilising and uptaking phosphorus and metal ions. The main citrates – Citrate Succinate Citrate Acetate and Citrate Lactate – are very effective at making phosphorus more soluble and mobile. This allows the plant to have a constant supply of bio available phosphorus during times of heavy flower production.

Now for the strange stories that you have read on the internet by a guy whom I believe is a crazy guy – a guy called G. Low

This guy is a journalist who used to work in a hydroponic store in Australia (maybe because he could not get work as a journalist>? ). He was used by several owners of different nutrient companies to make a scare campaign on the internet for a product called Super bud. This product was made by a company that I use to work for called Dutch Master….”

[End Quote]

 Ouch! “Crazy guy”?

Now for a dose of reality…



Daminozide is considered a hazardous substance according to OSHA 29 CFR 1910. 1200. The EPA lists daminozide as a “probable human carcinogen”. Combustion products include: carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides (NOx), and other pyrolysis products typical of burning organic material. Combustion may emit poisonous fumes. Daminozide is an S5 poison.


Daminozide is produced by reacting succinic acid ahydride with unsymmetrical dimethylhydrazine (UDMH also known as 1,1-Dimethylhydrazine). UDMH is toxic, a carcinogen and can be readily absorbed through the skin.
Although daminozide is the active ingredient, UDMH is also present as a contaminant in both technical and formulated products. UDMH can also be present in products through hydrolysis of daminozide and this increases as a function of time and increasing temperature. The formation of UDMH from daminozide residues is known to occur during cooking of apples and metabolism data has shown that daminozide hydrolyzes to UDMH in plants and in the mammalian body.

Daminozide was initially registered as a pesticide in the United States in 1963 for use on potted chrysanthemums. The first food use, apples, was registered in 1968.


In July 1984, the EPA initiated a ‘Special Review’ of pesticide products containing daminozide based on findings that daminozide and its degradate and metabolite, unsymmetrical dimethylhydrazine (UDMH), were oncogenic (caused the growth of tumors) at multiple organ sites, in multiple species and strains of test animals. The Agency issued a ‘Data Call-In’ in 1986 requiring additional toxicology and worker exposure data. As a result of the Special Review, the registrant, Uniroyal Chemical Company, voluntarily cancelled all food use registrations of daminozide on November 4, 1989. The EPA revoked the tolerances (maximum residue limits) for food uses in March 1990. There are no longer any registered food or feed uses of daminozide, and all tolerances have been revoked. The EPA had calculated the hazard of cancer among people exposed to UDMH in Alar for a lifetime is 45 per million, which is 45 times as high as the one-in-a-million hazard EPA considers “negligible.”


In fact, daminozide is perhaps one of the most controversial agrochemicals ever, eclipsed only by Agent Orange, after the “Alar scare” in 1989 in which a CBS 60 Minutes USA show labelled Alar “a potent human carcinogen”, resulting in the near bankruptcy of the US apple industry. Prior to 1989, five separate, peer-reviewed studies of Alar and its chemical breakdown product, UDMH, had found a correlation between exposure to the chemicals and cancerous tumors in lab animals. In 1984 and again in 1987, the EPA classified Alar as a probable human carcinogen.


The use of daminozide in any consumable crop is, therefore, illegal. The dangers it poses when used to grow a short-term decidious crop, which is then ingested via inhalation, are unknown.


Additionally, daminozide inhibits the gibberillin (GA) pathway at the late stages of gibberellin metabolism reducing terpenoid production in the forms of THC (D9-Tetrahydrocannabinol), CBN (cannabinol) and CBD (cannabidiol). In more simple terms, daminozide inhibits resin production and reduces quality.




Paclobutrazol was developed by ICI Chemicals, and registered by the U.S. Environmental Protection Agency and by the State of California as an injectable plant growth regulator for ornamental plants (not approved for food crops in the USA). Paclobutrazol diminishes plant growth through inhibition of gibberellin.


Paclobutrazol has long withholding periods (dependent on application rates and crop type). In some cases, control of growth may persist for more than one year. Typically, however, withholding periods are listed with registered paclobutrazol products at between 20 and 40 days.

Paclobutrazol (CASRN 76738-62-0) is classed as a herbicide/pesticide Plant Growth Regulator in the subclass of “Growth Retardant”. PBZ is an S5 poison. Its use is prohibited in many EU countries. The WHO lists paclobutrazol as “Moderately Hazardous”, while the US EPA lists it as “not classifiable as to human carcinogenicity” with:


“Substance Name — Paclobutrazol

This substance/agent has not undergone a complete evaluation and determination under US EPA’s IRIS program for evidence of human carcinogenic potential. “

[End Quote]

However, paclobutrazol has been shown to be toxic to the liver with:


“Based on the currently available toxicity information, DPR concluded that paclobutrazol causes adverse effects on liver function and developmental effects in rodents. DPR has further concluded that, in the absence of additional data to the contrary, paclobutrazol has the potential to cause similar effects in humans.” 1


[End Quote]

Paclobutrazol has been shown to be an environmental contaminant (Kathrin Reintjes et al 2006). In field situations, paclobutrazol is shown to have a half-life ranging from 3 to 12 months (Lever 1986) or 12 to 18 months, although some have reported persistence as long as 3 years (Jacyna and Dodds, 1995). Some commercial greenhouse operations have had issues dealing with chemical residues.2


The persistence of paclobutrazol in soil may result in contamination of nearby water bodies, thus presenting a possible hazard to human and animal health, and could also influence soil microbial activity with further effects on biodiversity.3


The hazards (if any) of using paclobutrazol on a short-term deciduous crop that is consumed via combustion (i.e cannabis) are completely unknown.


Paclobutrazol is a Gibberellin (GA) Biosynthesis inhibitor and therefore reduces terpenenoid production in the forms of THC (D9-Tetrahydrocannabinol), CBN (cannabinol) and CBD (cannabidiol). As with daminozide, paclobutrazol inhibits resin production and reduces quality.


  1. US EPA. Office of Pesticides and Toxic Substances and Californian Environmental Protection Agency
  3. Sybille Neidhart, Anuwat Jaradrattanapaiboon, Kathrin Reintjes,Berit Jöns, Martin Leitenberger, Joachim Ingwersen, Gunnar Kahl, Pittaya Sruamsiri,  Thilo Streck, and Reinhold Carl (2006) Which risks do result from the application of paclobutrazol in off-season mango production regarding residues in fruit and soil? First results of a long-term field study in northern Thailand

The Daminozide Money Trail


Let’s analyze for a moment how much money is made by those promoting PGRs as “rare earth elements”, “citrates”, “arginates”, “quinalone” (a new one to me), “humatic isolates”, “kelp” etc to unsuspecting consumers.

The math…

1 gram of pure substance in 1L equates to 1000ppm. Given Flower Dragon contains 18,400ppm of daminozide this equates to 18.4 grams per litre of daminozide at 100% purity in 1L solute (daminozide) + solvent (water) = 1L).
Recently, for the purpose of this article, I priced purchasing 100Kg of daminozide from a Chinese supplier. The product was 850 grams a kilo daminozide or 85% purity.


To achieve 18,500ppm of daminozide in solution with the Chinese product it would require 21.76g/L. Based on this, 1Kg of 85% daminozide would produce 45.95 litres of Flower Dragon. The price of the Chinese product at 100Kg was $97.00 USD per Kg. Add shipping and other costs to this and we could conservatively estimate that daminozide costs ex China $98.50 USD per kilo landed in BC, Canada where Flower Dragon is produced. Let’s be generous and make that $100 USD per 1Kg of daminozide. Therefore, 100 Kg of daminozide costs $10,000 USD ex China to BC. Don’t get hung up on the math. It’s largely irrelevant. The end result is the important thing (for those of you wishing to check my math feel free).

Okay, so we know that 1Kg of 85% daminozide produces 45.95 litres of Flower Dragon and 1Kg of daminozide costs $100 USD. Therefore 1L of Flower Dragon requires $2.17 of daminozide (I.e. 100 ÷ 45.95 = $2.17 USD).

Let’s also add twenty cents in Paclobutrazol (PBZ being cheap and used at low levels), $1.00 per plastic bottle used in production and $1.50 for labels. Total cost to produce 1L of Flower Dragon = $4.87 (round that off to $5.00 for ridiculously low levels of P and K that are also added in production).


100 kilo of 85% purity daminozide makes 4595.5 litres of Flower Dragon or 4595.5 1L bottles of saleable product. Total cost to produce equals $22, 977 USD based on $5.00 per bottle estimate.


Flower Dragon retails in the US for $120.00. We have 4595.5 1L bottles each retailing for $120.00. 4595.5 x $120.00 = $551,460.00 from an initial investment of  $22, 977. Therefore, the profit made along the way equates to $528,483.00 or roughly 2,300%.


Wholesalers typically mark up products 30% and retailers typically have markups of 100% on consumables. Based on this, Flower Dragon is sold to the wholesalers for about $45.00 (a $40.00 profit for Envy Plant Products or a 900% profit and $40 x 4595.5 = $183,820.00 on 100Kg of Daminozide = $165,4380.00 in profits); wholesalers then sell to retailers at $60.00 (4595.5 x $20 = $91,910) and finally retailers Flower Dragon to consumers for $120.00 (4595.5 x $60 = $275, 730).

Of course, I’ve oversimplified this somewhat because people have rents to pay etc. The aim, however, is to demonstrate the incredible sums of money that are made through the sales of these products.

What is most important to note here is the vast amount of profits generated all flow to the top of the daminozide pyramid. That is, wholesalers make 30%, retailers make 100% and Steve Berlow (Flower Dragon produced by Envy Plant Products – ex Dutch Master) and Craig Gribble (CEO of Dutch Master) make 900% on 100% of all Flower Dragon sales across the US and elsewhere. Technically speaking, this amounts to millions of dollars earned very quickly from lies, more lies, more lies, and banned for use in any consumable crop, daminozide (aka Alar).


Defining Toxic PGRs (subclass, “Growth Retardants”)

PGRs are without a doubt the hydro industries most controversial products. However, some misunderstanding surrounds them.


The term ‘Plant Growth Regulator’ covers a broad range of synthetic and natural (organic) PGRs. Just a few of these pose a risk to consumers while others are non-toxic.


In very simple terms chemical PGRs in the subclass of “Growth Retardants” such as daminozide (Alar), paclobutrazol, and chlormequat chloride are potential toxins while other Plant Growth Regulators such as Jasmonates (subclass, “Growth Inhibitor”) and Triacontanol (naturally found in alfalfa meal and classed as a plant growth stimulator) pose no risk at all.


Many PGR’s are hormones that are produced within growing plants themselves. Hormones are vital to plant growth and lacking them plants would be mostly a mass of undifferentiated cells. Because hormones stimulate or inhibit plant growth, many botanists also refer to them as plant growth regulators (PGRs). Botanists recognize six major groups of hormones: auxins, gibberellins, ethylene, cytokinins, abscisic acid, and brassinosteroids.


Auxins cause several responses in plants:

  • Bending toward a light source (phototropism)
  • Downward root growth in response to gravity (geotropism)
  • Promotion of apical dominance
  • Flower formation
  • Fruit set and growth
  • Formation of adventitious roots


Auxins (e.g. IBA, IAA, NAA) is the active in most rooting compounds in which cuttings are dipped during propagation (cloning). For instance, Clonex and other rooting compounds usually contain IBA (Indole-3-butyric acid) or NAA, or a combination of both.


Gibberellins stimulate cell division and elongation, break seed dormancy, and speed germination. The seeds of some species are difficult to germinate; you can soak them in a GA solution to help get them started.


Cytokinins are found in both plants and animals. They stimulate cell division. If a product is high in cytokinins and low in auxin, the plant will produce numerous shoots. On the other hand, if the mix has a high auxin to cytokinin ratio, the plant will produce more roots. Cytokinins are also used to delay senescence (aging and death).


Ethylene is found only in the gaseous form. It induces ripening, causes leaves to droop (epinasty) and drop (abscission), and promotes senescence. Plants often increase ethylene production in response to stress, and ethylene often is found in high concentrations within cells at the end of a plant’s life. The increased ethylene in leaf tissue in the fall is part of the reason leaves fall off trees. Ethylene also is used to ripen fruit (e.g., green bananas).


Abscisic acid (ABA) is a general plant-growth inhibitor. It induces dormancy and prevents seeds from germinating; causes abscission of leaves, fruits, and flowers; and causes stomata to close. High concentrations of ABA in guard cells during periods of drought stress probably play a role in stomatal closure.


Brassinosteroids are a new 6th generation plant growth hormone known as a steroidal plant hormone. Plants possess the ability to biosynthesize a large variety of steroids, but it was not until 1979 that a hormonal function was demonstrated in plants. Today, about 40 structurally and functionally related steroids, known as brassinosteroids, have been isolated from natural sources. Brassinosteroids demonstrate various kinds of regulatory activities in the growth and development of plants.


Other than naturally occurring plant hormones, other safe PGRs exist (e.g. Triacontanol) – just some of which can be found in various hydro industry products. It’s important to note this in order not to demonize all PGRs. Quite simply, when it comes to PGRs there are the good, the bad and the downright ugly. The latter (“downright ugly”) fall under the subclass of “Growth Retardants” and include daminozide, paclobutazol, chlormequat chloride, prohexadione, and uniconazole.


Identifying Chemical “Growth Retardants”


Any product that inhibits or stops upward growth and/or induces early flowerset is a product that should be avoided. This applies to both registered and non-registered products. For instance, through sleight of hand registration several PGR, “Growth Retardant” products are legally able to be sold through the hydroponics retail sector. These include, but are not limited to, Mr No, formerly Dr Nodes (0.4% paclobutrazol, sold in North America), Yield Masta/Sudden Impact (paclobutrazol and chlormequat chloride, sold in Australia and New Zealand), U-Turn (paclobutrazol, sold in Australia), Cyco Flower (paclobutrazol and chlormequat chloride, sold in Australia), and Bonza Bud (paclobutrazol, sold in Australia).


While the aforementioned products are registered, don’t be deceived – they are registered only for use on ornamental crops. For instance, U-Turn’s (APVMA reg 58890/100ml/0506) label states,




“For growth control of container grown ornamentals only as per directions for use.”


[End Quote]

As for Cyco Flower (Australia), another paclobutrazol containing product marketed with “APVMA approved PGR”, it’s APVMA registration, 64027/1L/0110, 64027/0110, reads,




“ Active Constituent/s: 4g/L paclobutrazol….For growth control of container grown ornamentals.”


[End Quote] 


And in the case of Dr Nodes (North America, 0.4% paclobutrazol, EPA registration number 80697-3), recently renamed Mr No, one hydroponic store notes,




“This product was designed specifically to shorten internodes, stop vertical growth, increases lateral growth and produce larger, more rigid flowers. This product is EPA registered for use on ornamental plants (i.e. bedding plants, flowering/foliage plants, woody plants or bulb crops).”


[End Quote]


Perhaps you’re getting the picture. I.e. The last time I checked PGR products sold through the hydroponics retail sector weren’t being sold to Geranium, Chrysanthemum, Poinsetta, Rhododendron, Camelia or Daffodil growers. Quite simply, paclobutrazol is not intended for use on ANY consumable crop (eaten, or ingested via inhalation).


The Problem


PGR based products halt the upward (apical) growth of a plant, thus giving cannabis growers control over the height of the plant and keeping nodes close and encouraging dense bud-set.


This is desirable for many indoor growers who wish to grow numbers of shorter plants (e.g. SOG and Coliseum/Vertical growing) or growers who work in areas with limited ceiling height.

Additionally, PGR products can increase yields where cannabis plants are grown in less than ideal conditions. This means that inexperienced growers or growers who fail to optimize their environments (temp, RH, airflow, nutrition) can achieve higher yields when using PGRs. This said, where growers do optimize environments, PGRs in the subclass of “Growth Retardants”, such as daminozide and paclobutrazol are likely to reduce yields.

PGR products are often popular with large commercial cultivators. Large commercial cultivators are responsible for large amounts of commercially available cannabis. As a result, many cannabis consumers are unwittingly purchasing potentially PGR tainted cannabis throughout Australia, North America, the UK, and Europe.


In Australia, where PGR flowering additives first became available through hydroponic stores, large numbers of cultivators now produce cannabis using PGRs. The US and other countries are in danger of mirroring this situation.


The illicit status of cannabis and the high profits associated to the cultivation and sale of cannabis creates a situation that doesn’t lend itself to a strong code of ethics amongst some cultivators and suppliers (this statement extends to elements within the med industry, including growers/suppliers and dispensaries). Due to this, even when cannabis growers are aware that PGR products may contain potentially harmful actives some will choose to use them regardless. In short, only a reprobate would choose to use PGRs without warning their clients/consumers that this is the case (would you like Alar with that?). This said, the cannabis culture, due to the illegal status of the “drug”, attracts more than its fair share of reprobates. Quid pro quo!


Let’s not lose sight of the fact that greed can be a powerful motivator.


Sadly, many PGR proponents/users who contaminate medicine with carcinogenic chemicals would also pass themselves off as “care givers” (the author knowing several such people). Arguments put forward by PGR proponents include cannabis is a carcinogen (which is incorrect) and, therefore, growing with a “potential” carcinogen and then selling the produce to unsuspecting consumers shouldn’t be an issue (your mother must be very proud of you!); or, the product I use that immediately ceases upward growth isn’t proven to be a PGR (you’ve just “proven” it you dickhead); or, PGRs aren’t an issue if you use them 30 days before harvest (and you would know this how?); or, the potential risk of harm to consumers is outweighed by the gains (financially of course – you’re making Monsanto look very good!); or, no one has proven to me that PGRs are dangerous (this is hardly the point – all evidence suggests their use is problematic and it isn’t up to regulators to prove agrochemicals are dangerous, but instead up to the companies who sell/develop these products to prove they are safe before putting them to market).


Additionally, the hydroponics retail industry is an industry that remains largely unregulated. This has enabled unethical manufacturers, wholesalers and retailers to act unhindered by regulatory codes/consumer protection policies. In fact, the hydroponics industry is guiltier than most. In spite of the evidence, some of the largest wholesalers (e.g. Sunlight Supply, US) continue to openly distribute cannabis specific PGR products which they must know contain potentially harmful actives. Further, they distribute these products via highly deceptive marketing with doctored MSDS (I.e. failing to list actives).
Similarly, the med industry is one that remains unregulated. This situation means that medicinal users – just some of whom are amongst societies most vulnerable – remain largely unprotected by unscrupulous operators.


Sadly, many of these PGR proponents who contaminate medicine with carcinogenic chemicals would also pass themselves off as “care givers” (the author knowing several such people).

Furthermore, a legal paradox comes into play (Catch 22). That is, it is illegal to use daminozide and/or PBZ on ANY consumable crop. This said, cannabis is an illegal crop and is, therefore, not legally recognized as a consumable crop (even though it is consumed by millions of people worldwide and is deemed by authorities to be the largest consumable cash crop in many parts of the world where officially the same authorities deem it not officially consumed… wow!). Due to this, cannabis consumers are not consuming a consumable crop… As a result, regulating the sale of long banned daminozide and other PGRs for use on “any consumable crop”, through the hydroponics industry, becomes an administrative black hole.


Take for example our recent case. Daminozide and PBZ are banned for use in any consumable crop under EPA law. However, while California acted, based on fertilizer registration laws, the EPA and/or FDA whose brief it is to police the use of daminozide and PBZ on consumable crops are nowhere in sight.  Theoretically, this means that if Flower Dragon, Phospholod and others were registered for use on non-consumable crops, listed actives, perhaps gave instructions for use with geraniums and provided safety instructions and MSDS they could be made legally available through Californian et al hydro stores. Of course, we all know that at $120 a pop geranium growers would be knocking down hydro store doors (call me sardonic – i.e. characterized by irony, mockery or derision). This aside, officially, no one is using daminozide or PBZ to cultivate cannabis – a widely consumed crop. Confused yet? …. so am I!

Additionally, while daminozide containing products are now banned in California and Oregon they remain widely available in other US states (et al). This of course means that daminozide products remain available throughout the US because anyone in California and Oregon can purchase interstate, via the internet, and have Flower Dragon, Phosphoload or any of the other numerous PGR products delivered to their door. In fact, the CDFA informs me that they are unable to police interstate deliveries.

Feasibly, many millions of cannabis consumers, on a global basis, are being exposed to cannabis grown with chemical PGRs. Given that 40% (125,000,000) of American’s are estimated to have smoked cannabis in their lifetimes, with a percentage of these being regular users, the US alone accounts for millions of cannabis consumers who may be exposed to cannabis grown with PGRs. As med users are typically regular consumers, who often purchase from multiple sources (different strains from the same dispensary coming from multiple sources of origin etc), this places them at high risk.


What do we actually know about the outcomes of using PGRs on a short-term deciduous crop that is ingested via combustion? We know that many PGRs have long withholding periods. We know that no hydro industry PGR product has been registered with the appropriate efficiency data to support its safety for the purposes which it is meant (sleight of hand registrations for use on pot grown ornamentals discarded). In the case of daminozide, we know that it was banned in 1989 due to its potential as a human carcinogen, while in the case of PBZ we know that it is registered for use on potted ornamental plants only and has been linked to causing liver disease.


A few callous manufacturers (reprobates thinly disguised as businessmen) slapped systemic pesticides into bottles, promoted them with the most reprehensible marketing conceivable (poisons thinly disguised as organic) and began playing Russian roulette with the lives of cannabis consumers. Call it for what it is….


Reducing Stretch Naturally (without PGRs)


Various factors such as plant hormones, light intensity and colour, thermoperiod (the difference between night and day temperatures), carbon acquisition, and nutrients influence the amount of stretch a plant will exhibit during its life cycle. Because of this, plant stretch can be greatly reduced if the right growing practices are implemented in the grow room. For instance, due to the toxic nature of PGRs, much research surrounding reducing stem elongation in various crops has been conducted in the past several years. This research has demonstrated several things:


  1. Light colour spectrum and intensity play an important role in reducing stretch
  2. Ensuring adequate plant spacing is critical to reducing stretch. i.e. plants that are placed too close to one another are forced to compete for light and this results in shade avoidance syndrome (SAS). As a result of SAS the plants stretch
  3. Thermoperiod (the difference between night and day temperatures, termed ‘DIF’) can be manipulated in such a way as to greatly reduce stretch. For example, studies show that stretch can be reduced by approximately 30% by reducing the morning temperature below that of the night temperature for approximately the first 3 hours after the lights turn on.
  4.  Mechanical stresses such as repeated brushing, shaking, or bending caused by air movement or contact with animate or inanimate objects can reduce plant growth. A study conducted by Dr. J Latimer demonstrated the commercial potential of this technique for controlling the height of vegetable transplants, particularly tomato. This work was initiated, in part, by the fact that the chemical PGR, B- Nine  (85% daminozide) was deregistered for use on consumable crops. One system of mechanical conditioning adapted to commercial greenhouses involves drawing a bar across the tops of the plants once or twice a day. The bar is set low enough to contact the plants, but not so low that the plants are injured or uprooted. 30 to 40% reductions in height have been reported with this system.
  5. Fertilization influences stretch. For example, low phosphorus levels during the stretch cycle will promote compact plants while higher phosphorus levels will promote stretch
  6. Plant hormones (phytohormones) such as cytokinins and jasmonic acid (methyl jasmonate) reduce stretch



SCROG (Screen of Green)


Scrog is a term used in the indoor growing of cannabis. The plants grow up to the screen and then are “trained” or tied to the screen, resulting in a flat table of plant growth. Through this means plants can be trained/tied out to remain shorter than they normally would grow. Another advantage to scrogging is because all the buds are growing at about the same height, it is possible to get all the growth within the effective circle of light from the lamp, resulting in increasing yields within a given space.




Apical dominance (stretch) is caused by the apical bud (top shoot of the plant) producing IAA (auxin) in abundance.


When the apical bud is removed, the source of IAA is removed. Since the auxin concentration is much lower, the lateral buds (side shoots) are stimulated to grow. Thus, decapitating (pruning) the top of the plant will cause it to branch, reducing upward growth.


Due to this tipping/topping is a good technique, along with scrogging, to control plant height.


Flipping Times and Understanding the Genetics You Work With


This is a tricky one as different people will use different techniques of growing. Some people will grow small plants in numbers while others will grow just one large plant etc. Also, different plants (genetics) will do different things. One type of plant may be very explosive and another type may not have the same vigor. One strain may be far leggier than another. Getting to know your strain will help you fine-tune the finishing height.


As a rule of thumb – the plant does 80% of its growing during the 12 hr light cycle. So be wary. Don’t think that you have to grow a plant in the 18-hour light cycle for too long. As a general rule if you switch down an 8 – 10inch plant you will finish with a 2 1/2 to 3-foot plant.


Know your plant and flip at the appropriate time!


Genetics! Genetics! Genetics!


Genetics play a major role in plant characteristics/traits. In very simple terms, sativas are a much ‘leggier’ plant than indicas and hence indicas, or indica dominant indica/sativa crosses are better suited to indoor growing environments.




The light energy required by plants is confined almost entirely to the visible spectrum of light (400nm – 700nm). While there are key points within this spectrum (435nm and 675nm etc), growth is optimized under the entire range of the spectrum. This is because different color wavelengths stimulate different biochemical reactions within the plant. As a result of this, different physiological functions are activated and energized, which – in turn – determine plant growth rates and formation characteristics.


Photosynthesis depends on the energy created by a combination of both light intensity and color.


Growers who have experimented with different lighting combinations can/will tell you that different lighting configurations can produce very different results. For instance, plants that are flowered under a combination of red spectrum (HPS) and blue spectrum (MH) lighting form very differently than plants that are flowered under red spectrum light alone.


In simple terms, blue light (400 to 500 nm) has been shown to have an inhibitory effect on stretch,[1] whereas red light, particularly red/far red light at 660:730 nm[2], has been shown to increase stretch.


This means that lamps which possess higher degrees of blue spectrum light and lower levels of red spectrum light are more ideal for use during the stretch cycle.  For example, in one study with tomato (2013) it was shown that plant height and internode length was highest in plants that were grown under HPS (52.2cm height and 5.1cm internode length) while the most compact plants were grown under lights that had the highest blue fraction (21.4cm height and 2.8cm internode length). [3]  In another study (1997) where soy bean plant height and artificial lighting were compared (HPS v. MH) in controlled environments, including hydroponics, plant height was reduced from 46 to 33 cm when plants were grown under metal halide lamps compared to high pressure sodium lamps at the same photosynthetic photon flux.[4] In yet another study (2002), the effectiveness of two types of far red light absorbing greenhouse films in reducing stem elongation of cucumber, tomato, and bell pepper seedlings was investigated. Both FR light absorbing films were effective in reducing stem elongation in cucumber, bell pepper, and tomato seedlings.[5]


Read more about lighting to reduce stretch here….


[1] Shimizu H. Ma Z. Tazawa S. Douzono M. Runkle E. S. Heins R. D. (2005) Blue Light Inhibits Stem Elongation of Chrysanthemum

[2] Pausch, R.C., S.J. Britz, and CL. Mulchi, Growth and Photosynthesis of Soybean (Glycine mux (L.) Merr.) in Simulated Vegetation Shade: Influence of the Ratio of Red to Far-Red Radiation, Plant, Ceil and Env.,

[3] Kotriana, S. (2013) The effect of light quality on tomato (Solanum lycopersicum L. cv ‘Efialto’) growth and drought tolerance

[4] Dougher T. A. 0. and Bugbee B. (1997)  EFFECT OF LAMP TYPE AND TEMPERATURE ON

DEVELOPMENT, CARBON PARTITIONING AND YIELD OF SOYBEAN, Adv. Space Res. Vol. 20, No. 10, pp. 1895 -1899.1997

[5] Rajapakse N. C. and Li S (2002) Exclusion of Far Red Light by Photoselective Greenhouse Films Reduces Height of Vegetable Seedlings


Quality (Essential Oil) and Light Colour Spectrum


An important point to consider also, when discussing light types that are most suitable for indoor growing, is that essential oil production is stimulated by a wide range of light colour spectrums and, therefore, the combination of HPS and MH lighting better promotes essential oil production than HPS alone. For example, research shows that a combination of blue light and red light promotes more flavonoid synthesis than where predominantly blue light or predominantly red light are used alone; however, other wavelengths and possibly ratios between wavelengths also have an effect. For example, one study compared multiple artificial light types and found that maximum flavonoid synthesis occurred under a continuous lighting spectrum of 400 – 750 nm.[1]


What this really means is that the all too common cultural practice of using high pressure sodium (HPS) lighting alone in indoor growing has played a significant role in promoting stretch and reducing quality.


What this also means is that plants are ideally grown under MH lights (or other lamps that are high in blue spectrum – e.g. LED grow lights) during the settling, vegetative and stretch phases and thereafter a combination of MH and HPS lighting will provide the best results where yields and essential oil production are concerned


[1] Kotriana, S. (2013) The effect of light quality on tomato (Solanum lycopersicum L. cv ‘Efialto’) growth and drought tolerance


Shade-Avoidance Syndrome (SAS) – Plant Spacing


One of the most common mistakes made by indoor growers is that they fail to appreciate that fewer plants can mean more yield. Too many plants crowded into a small space will compete for available light and as a result stretch as they compete for light. This is called shade avoidance syndrome (SAS) where plants respond to competition signals generated by neighbors by evoking SAS, which results in stem elongation, increased internode distance, altered flowering time and reduced shoot branching. [1] Basically, what happens with SAS is a plant grown under canopies of other plants perceives the reduction in the ratio of red (R) to far-red (FR) light as a warning of competition, and enhances elongation growth in an attempt to overgrow its neighbors. As a result, plants stretch in order to compete with one another for light. [2] As Morelli et al (2000) put it: “The most dramatic shade avoidance response is the stimulation of elongation growth.”[3] This results in stretch and less than optimal yields.


Therefore, it is imperative that plants aren’t overcrowded and competing for light. This means that appropriate plant spacing needs to be considered as an optimal growing practice.

[1] Krishna Reddy S, Finlayson SA (2014) Phytochrome B promotes branching in Arabidopsis by suppressing auxin signaling. Plant Physiol. 2014 Mar;164(3):1542-50. doi: 10.1104/pp.113.234021. Epub 2014 Feb 3. See also Ronald Pierik and Mieke de Wit (2013) Shade avoidance: phytochrome signalling and other aboveground neighbour detection cues

[2] Carabelli M, Possenti M, Sessa G, Ciolfi A, Sassi M, Morelli G, Ruberti I. 2007. Canopy shade causes a rapid and transient arrest in leaf development through auxin-induced cytokinin oxidase activity. Genes and Development 21, 1863–1868.

[3] Morelli G, Ruberti I. 2000. Shade avoidance responses. Driving auxin along lateral routes. Plant Physiology 122, 621–626.



Thermoperiod – Manipulating Night and Day Temperatures to Reduce Stretch


The difference in temperature during the day/night (light/dark) period, known as “thermoperiod”, has a major effect on plant growth and architecture.


Through manipulating these temperatures in the right manner stretch can be greatly reduced.


Gibberellins, Stretch and Thermoperiod


Gibberellins (GA) are the plant hormone most associated to stretch. For example, many chemical PGRs (e.g. paclobutrazol, chlormequat chloride and daminozide/Alar) reduce the bioactive GA levels in plants and through this mode of action reduce stretch.


However, with gibberellins in mind, studies have shown that where day temperatures are lower than night temperatures endogenous GA levels are reduced in plants, and as a result stretch is reduced.[1] Which brings us to DIF.




DIF stands for the difference between ‘day temperature’ (DT) and ‘night temperature’ (NT). This can be expressed as either an equal, positive or negative number. For example night 22.40C (72.40F), day 280C (82.40F), equates to positive DIF (DIF = + 5.60C or +100F). Conversely, night 280C (82.40F), day 22.40C (72.40F) equates to negative DIF (DIF = – 5.60C or -100F).  Additionally, there is equal DIF (also referred to as “zero DIF”) which is when the day and night temperature are the same.


Stem elongation is promoted by warmer days than nights (+ DIF) and inhibited by warmer nights than days (- DIF). Plants become taller as DIF becomes more positive and plants become shorter as DIF becomes more negative. Therefore, plants grown under a positive DIF are taller than plants grown at an equal DIF, and plants grown under an equal or zero DIF are taller and have larger internode gaps than plants grown under a negative DIF.


As a result, a negative DIF treatment (low DT and high NT) is a tool to produce compact plants with short internodes without a delay in production time. For example, in a study by Maas et al (1996) it was shown that stem elongation in Fuchsia x hybrida was influenced greatly by cultivation at different day and night temperatures. Internode elongation of plants grown at a DT (25°C), NT (15°C) difference (DIF+10°C) was almost twofold of that of plants grown at the opposite temperature regime (DIF-10°C).[2]


The negative DIF technique is so effective it has largely replaced the use of chemical PGRs in a number of commercially produced crops.[3]


‘Morning Temperature Dip’ or ‘Cool Morning Pulse’ Technique 


Negative DIF, like chemical PGRs, has its greatest effect on height during the phase of most rapid stem elongation. Therefore, negative DIF is most effective when applied during the stretch phase of the crop cycle (e.g. first 2 – 3 weeks or so of the 12/12 light cycle). Further, studies show that the most active phase of stem elongation in plants occurs at the end of the dark period and during approximately the first 2-3 hours after the sun rises. Therefore, stretch can be reduced through reducing the morning temperature (when lights first come on) below that of the nighttime temperature for approximately 2 -3 hours. Studies have shown that lowering the temperature for a two hour period starting 30 minutes prior to dawn is almost as effective as maintaining negative DIF throughout the entire day.[4] This technique is called the “morning temperature dip” technique or the “cool morning pulse.”


Although research findings are variable, there is a general consensus that many plants are sensitive to a temperature dip during the first 2 to 4 h of the photoperiod.[5] For example, a temperature dip given during the first 2 hours of the day reduced internode length of cucumber and tomato seedlings.[6] Plant height in this study was reduced in direct response to the degree of the morning temperature dip (between -2 and -10oC).


In research by Ueber and Hendriks (1992) it was shown as a response to a 2 hour temperature drop from 24 °C to 8 °C (DIF = – 16°C) in the morning, stem elongation was reduced by more than 50% in poinsettia. Conversely, a moderate temperature drop from 24 to 16°C (DIF = – 8°C) reduced plant height by between 5 and 25% depending on duration.[7]


It is important to note, however, that optimum negative DIF treatment is crop dependent. For example, ester lilies’ show the greatest effect at a DIF of -15°C, poinsettias at -16°C, and fuchsia at -20°C.   Additionally, tomato, corn, and cucumber have strong responses to DIF, while squash, watermelon, pea, and bean are less responsive.[8]


Other than this, negative DIF can elicit other not sort after growth responses if handled incorrectly. For instance, leaf chlorophyll content is reduced in plants grown with a negative DIF.[9]  Reduced leaf chlorophyll results in reduced rates of photosynthesis (chlorophyll is the key molecule responsible for light absorption in plants and therefore pivotal in photosynthesis) and can result in visibly chlorotic plants (yellowing and/or dying leaves). However, negative DIF-induced leaf chlorosis is typically reversible, with plants greening rapidly after removal from the negative DIF environment.[10] Therefore, reducing the day temperature to accommodate negative DIF also reduces the growth rate in heat-loving plants and too excessive a negative DIF (temperature and/or duration) has been demonstrated to reduce relative flower number and size in several species. Additionally, leaves on plants grown with a negative DIF tend to point downwards while those grown with positive DIF point upward.


Therefore, some cautious experimentation is advised where working with the morning temperature dip (in commercial growing applications maximum negative DIF is usually no more than – 6°C).

My Experiences with the Morning Temperature Dip Technique – Recommendations

Firstly, ideals when using the morning temperature dip technique seem to be somewhat genetic dependent. That is, some strains respond far more to the technique than others.


However, I find when growing under metal halide lamps, during stretch, that by maintaining equal DIF (same night and day temperature) and then a 3-5°C drop one hour before and two hours after the lights turn on (total 3 hours negative DIF) does the job nicely with most genetics. This said your genetics may differ and want more or less. Therefore, begin conservatively with equal night and day temperatures and a moderate temperature dip (e.g. 3°C) and see where this takes you. If the reduction in stretch isn’t enough increase the DIF in small increments until you achieve the desired result. i.e. to increase the inhibitory effect of a temperature drop on stem elongation, you can either extend the period of the temperature drop or increase the degree of the temperature drop.[11]  Conversely, to decrease the inhibitory effect of temperature drop on stem elongation decrease the period of the temperature drop or reduce the degree of the temperature drop.


Most importantly, if choosing to use the morning temperature dip technique, watch the plants closely for early signs of chlorosis (leaves – particularly older leaves – will lose their dark green hue and begin paling and going yellow). If signs of chlorosis do appear than restore normal night and day temperatures (i.e. cooler nights than days).


By the way, I have refined the equal/zero DIF and negative morning temperature dip technique to achieve about a 30% reduction in stretch in several strains.


Author’s note: some growers report that they get the desirable reduction in stretch by running equal DIF alone (i.e. equal DIF with no morning temperature dip). Again. I have found the reduction in stretch elicited by equal DIF and/or the morning temperature dip does tend to be genetic dependent and different strains may require different approaches. However, you may find that by running equal DIF alone this provides you with the sort after or, at least, acceptable growth responses.


Use Negative and/or Equal DIF During the Stretch Phase Only


It is commonly asserted by authors on the subject of plant growth (myself included) that plants require a higher daytime to nighttime temperature (positive DIF) to achieve optimum yields. This stands true! However, this assertion is perhaps overly simplistic when considering stem elongation in certain flowering/fruiting crops. For example, having covered thermoperiod and DIF we can see that equal DIF or negative DIF (or combinations thereof) during the stretch phase can be beneficial to plant architecture and yields.


This said, the scientific community has long understood that growth and yields in many plant species are best stimulated by higher day and lower night temperatures.


This comes down to photosynthesis, respiration and thermoperiod DIF.


Thermoperiodic plants (e.g. tomato, cucumber, capsicum, chilli) produce maximum growth when exposed to a day temperature that is about 5 to 10°C higher than the night temperature. This allows the plant to photosynthesize (build up sugars) and respire (break down sugars) during an optimum daytime temperature, and to curtail the rate of respiration during a cooler night. Too high night temperatures cause increased respiration, sometimes above the rate of photosynthesis. This impacts on growth and yields. Put simply, thermoperiodic plants typically produce the highest yields when day temperatures are higher than night temperatures.  For example, optimum flowering of tomato plants occurs under the conditions of a positive DIF at 25oC DT and 15oC NT (DIF = +10oC).[12]


Conversely, negative growth responses can be elicited through diverging from thermoperiod ideals. For example, we have seen that a negative DIF results in reduced chlorophyll content in the leaves of plants, and reduced leaf chlorophyll results in reduced rates of photosynthesis.  In turn, reduced photosynthesis results in reduced growth. This is just one reason that negative DIF works to reduce stem elongation. Technically, by manipulating the thermoperiod to negative DIF we slow the plant down (i.e. reduce its growth rates during a period of rapid upward growth and stem elongation), which results in a more compact plant with closer internodes.  While slowing growth may be desirable during stretch we don’t want to slow growth down during e.g. the swelling phase when the flowers are forming and growing (swelling). Therefore, once negative DIF has done its job to reduce stretch we want to encourage growth as much as possible by increasing the photosynthetic capacity/potential of the plant as much as possible. This is done by, among other things, having a positive DIF where day temperatures are 8 -10oC higher than night temperatures.


Therefore, while an equal or negative DIF, or combinations thereof, may be beneficial during the stretch phase of the crop cycle (for inhibiting stem elongation and reducing internode distance) equal or negative DIF will prove detrimental to yields thereafter. For this reason, only use equal or negative DIF during stretch (i.e. the first 2 – 2 1/2 weeks or so of the 12/12 light cycle). After this, run a positive DIF with days (lights on) approximately 8 – 10oC warmer than nights (lights off).



[1] Jon Anders Stavang, Bente Lindgård, Arild Erntsen, Stein Erik Lid, Roar Moe, and Jorunn E. Olsen:

Thermoperiodic Stem Elongation Involves Transcriptional Regulation of Gibberellin Deactivation in Pea, Plant Physiol. Aug 2005; 138(4): 2344–2353. See also Jensen E.  Eilertsen S.  Ernsten A. Juntilla O and Moe R: Thermoperiodic control of stem elongation and endogenous gibberellins in Campanula isophylla, Journal of Plant Growth Regulatation October 1996, Volume 15, Issue 4, pp 167 – 171

[2] Frank M. Maas, J. Hattum (1996) The Role of Gibberellins in the Thermo- and Photocontrol of Stem Elongation in Fuchsia

[3] Jon Anders Stavang, Bente Lindgård, Arild Erntsen, Stein Erik Lid, Roar Moe, and Jorunn E. Olsen:

Thermoperiodic Stem Elongation Involves Transcriptional Regulation of Gibberellin Deactivation in Pea, Plant Physiol. Aug 2005; 138(4): 2344–2353.

[4] Douglas A. Bailey, Professor and Brian E. Whipker, Height Control of Commercial Greenhouse Flowers, NC State University, Department of Horticultural Science retrieved 12/14 at

[5] Myster, J. and R. Moe. 1995. Effect of diurnal temperature alternations on plant morphology in some greenhouse crops a mini-review. Scientia Hort. 62:205-215.

[6] Grimstad, S.O. 1993. The effect of a daily low temperature pulse on growth and development of greenhouse cucumber and tomato plants during propagation. Scientia Hort. 53:53-62.

[7] Ueber E and Hendriks L. (1992)  Effects of intensity, duration and timing of a temperature drop on the growth and flowering of Euphorbium pulcherrima Willd. ex Klotzsch. Acta Horticulturae 1992;327:33-40.

[8] Erwin, J.E. and R.D. Heins. 1995. Thermomorphogenic responses in stem and leaf development. HortScience 30(5):940-949.

[9] Berghage, R.D., J.E. Erwin, and R.D. Heins. 1991. Photoperiod influences leaf chlorophyll content in chrysanthemum grown with a negative DIF temperature regime. HortScience 26:92.

[10] Erwin, J.E. and R.D. Heins. 1995. Thermomorphogenic responses in stem and leaf development. HortScience 30(5):940-949.

[11] Ueber E, and Hendriks L (1992) Effects of intensity, duration and timing of a temperature drop on the growth and flowering of Euphorbium pulcherrima Willd. ex Klotzsch. Acta Horticulturae 1992;327:33-40.

[12] Downs R. (1975) Environment and the Experimental Control of Plant Growth pp. 25, Academic Press


Mechanically-induced stress (MIS)to Reduce Stretch


‘Mechanically-induced stress’ (MIS), also termed ‘mechanical handling’, occurs in nature as the above ground parts of plants are moved, usually by wind, but also by such things as rain, people and animals. It can be induced indoors by various actions such as directing oscillating fan air directly at the plants, rubbing or bending the stems or shaking (“seismomorphogenesis”) or brushing or rubbing (“thigmomorphogenesis”) the entire plant. The most noticeable effect of MIS is a reduction in stem, leaf or petiole length, invariably resulting in plants that are more compact with closer internode distance than unstressed controls. [1]


The Growth, Stress Response and MIS  


The effects MIS elicits in plants basically comes down to the growth, stress response where plants under stress sacrifice growth and instead direct energy towards dealing with biotic or abiotic stressors. This growth, stress response can be used to our advantage to reduce stretch and encourage closer internode distance.


I’ve covered some material on the growth, stress response when discussing the phytohormone jasmonic acid on page…


To repeat and abbreviate this material, growth and defense tradeoffs are thought to occur in plants due to ‘biotic’ (i.e. living disturbances such as fungi and pests) and ‘abiotic’ (i.e. factors that occur in nature such as high temperatures, drought, extreme sunlight and high UV) stresses, which demand prioritization towards either growth or defense, depending on external and internal factors. These tradeoffs have significant implications to growth because both processes are vital for plant survival, reproduction, and, ultimately, plant health.


While many of the molecular mechanisms underlying growth and defense tradeoffs remain to be fully understood, phytohormone cross-talk has emerged as a major player in regulating the balance between growth and plant defense. Just two of the phytohormones that are shown to be effected by stress are gibberellins and ethylene.


Studies have demonstrated that MIS techniques such as brushing or shaking plants stimulates ethylene production[2] and reduces endogenous gibberellin levels.[3]


Higher ethylene levels result in decreased stretch and closer internode distance. For example, when discussing the chemical PGRs that reduce stretch, an example of one such PGR is ethephon. Unlike other PGRs, ethephon does not inhibit gibberellin or brassinosteroid biosynthesis. Instead, plants take up ethephon where it is converted to ethylene in plant cells. The increased ethylene causes cells to limit elongation and increase in width. Besides this, the release of ethylene can also reduce apical dominance, which promotes axillary branching.  Theoretically, plants release a small amount of the plant hormone ethylene when they are touched or moved (by people, the wind, etc.). With repeated and frequent plant movement, plants release enough ethylene to inhibit elongation. Research has shown that plants generally respond in a quantitative manner to the number of times they are brushed or shaken: The more frequent the brushing or shaking, the more suppression of stem elongation. This suggests that brushing or shaking plants is similar to repeatedly providing a very low concentration of ethephon to plants.


Gibberellins (GAs) are the hormone most associated to promoting plant stretch. Research has shown that MIS reduces endogenous GA levels and, thus, acts to reduce stretch. For example, in research by Zeng et al (2006) it was concluded;




“…plants treated 30 days after planting with mechanical stress by brushing for 30 days, produced more ethylene on the third day and maintained high ethylene production, while control plants had low ethylene levels throughout the experiments. Gibberellic acid (GA)-like substances in the control plants were separated into 4 bands on silica gel TLC plates. At the same Rf of authentic GA1, GA3, and GA7, GA1- and GA3-like substance contents decreased markedly in brushed plants compared with the control plants. This result suggests that mechanical stress reduced stem elongation of chrysanthemum is affected by the activity of GA and ethylene production.” [4]


(End Quote)


MIS has been found to be a very effective way of controlling plant height (30% to 50% reductions have been recorded) of many vegetable transplants and herbs. The MIS brushing technique involves the movement of a PVC pipe, wooden dowel rod, aluminium or steel bar, or burlap bags over the top third of the plant. Research at the University of Georgia suggests that plants should be brushed daily for about 40 strokes to obtain the greatest effect. The foliage should be dry to avoid damage to the leaves. The effects of brushing on plant growth dissipate within three to four days after you stop applying the treatment.


Other than plant brushing, MIS can also be effectively applied by shaking plants. The general effect of shaking plants is retardation of internode elongation and inhibition of leaf expansion, which dwarfs plants in size and mass, depending on the dose of stress received.[5]


In addition to growth control, MIS affects other plant characteristics. Specific chlorophyll content is higher in MIS treated tomato,[6] eggplant,[7] lettuce and celery.[8] In addition, MIS increases specific leaf weight of tomato, eggplant, lettuce, celery, and cauliflower. Increased chlorophyll levels results in darker green leaves and healthier looking plants.


MIS also increases stem and petiole strength. For example, analysis of stem structural components showed increased percent of cellulose in the fiber component of shaken tomato stems.[9]


Studies have shown extremely good results in MIS treated crops. Brushing several cultivars of tomato transplants daily inhibited stem elongation by 30% to 37% compared to nontreated plants and either decreased or did not affect stem diameter.[10] However, stems of the treated plants were tougher and more elastic than those of the controls. Liptay (1985) noted that vibration reduced tomato seedling stem length by 40% and decreased stem diameter by 14%.[11] In research by Samimy (1993) where plexiglas was used to impede tomato seedling vertical growth impedance reduced stem length of 29-day old tomato seedlings by 21% and increased stem diameter by 20%.[12] In a study by Hidayatullah where MIS was introduced by pruning yield increase in relation to control was up to 61% higher. This was attributed to a decrease in endogenous GA level at blooming and fruiting stages and increase in IAA levels at flower initiation, blooming and fruiting stages.[13]


[1] Biddington N. L. (1986) The effects of mechanically-induced stress in plants — a review, Plant Growth Regulation, 1986, Volume 4, Issue 2, pp 103-123

[2] Mensuali-Sodi, A., Serra, G., Veiga de vincenzo, M.C., Tognoni, F. and Ferrante, A. 2006. ETHYLENE RESPONSE TO MECHANICAL STRESS PERTURBATION OF SALVIA SPLENDENS L. POTTED PLANTS . Acta Hort. (ISHS) 723:421-426 See also Biddington N. L.The effects of mechanically-induced stress in plants — a review, Plant Growth Regulation, 1986, Volume 4, Issue 2, pp 103-123

[3] Zheng C. Wang W. and Hara T. (2006) Mechanical Stress Modifies Endogenous Ethylene and Gibberellin Production in Chrysanthemum

[4] Zheng C. Wang W. and Hara T. (2006) Mechanical Stress Modifies Endogenous Ethylene and Gibberellin Production in Chrysanthemum

[5] Mitchell C. A. (1996) Recent Advances in Plant Response to Mechanical Stress: Theory and Application

[6] Mitchell, C.A., C.J. Severson, J.A. Wott, and P.A. Hammer. 1975. Seismomorphogenic regulation of plant growth. J. Amer, Soc. Hort. Sci. 100:161-165

[7] Latimer, J.G. and C.A. Mitchell. 1988 Effects of mechanical stress or abscisic acid on growth, water status, and leaf abscisic acid content on eggplant seedlings. Scientia Hort. 36:37-46.

[8] Biddington, N,L. and A.S. Dearman 1985. The effect of mechanically induced stress on the growth of cauliflower, lettuce and celery seedlings. Ann. Bot. 55:109-119.

[9] Latimer J. G. Mechanical Conditioning to Control Height, HortTechnology October – December 1998 8(4)

[10] Johjima, T., J.G. Latimer, and H. Wakita. 1992. Brushing influences transplant growth and subsequent yield of four cultivars of tomato and their hybrid lines. J. Amer. Soc. Hort. Sci. 117:384-388. See also Latimer, J.G. and P.A. Thomas. 1991. Application of brushing for growth control of tomato transplants in a commercial setting. HortTechnology 1:109-110.

[11] Liptay, A. 1985. Reduction of spindliness of tomato transplants growth at high density. Can. J. Plant Sci. 65:797-801.

[12] Samimy C. Physical Impedance Retards Top Growth of Tomato Transplants. HORTSCIENCE 28(9):883-885. 1993.

[13] Hidayatullah, Asghari  Bano and Mansab Ali Khokhar (2013) Phytohormones Content in Cucumber Leaves by Using Pruning as a Mechanical Stress

Low Phosphorus in Solution to Reduce Stretch


This one may not be viable for recycling growers, nor perhaps hobby growers who purchase off the shelf hydroponic nutrients in general. However, we’ll cover low phosphorus in solution as a means for reducing stretch for several reasons; 1) this is shown to be an extremely effective strategy for reducing stretch; 2) providing low phosphorus to the plants is viable for those who formulate their own hydroponic nutrients and; 3) at some point a hydroponic nutrient manufacturer may release a liquid fertilizer geared towards use during the stretch cycle with the aim of reducing stem elongation. This fertilizer, no doubt, will contain low phosphorous.


The Science of Low P and Stretch Reduction     


Many commercial agricultural growers have traditionally used fertilization to promote stem elongation (promote taller plants) and believed that the elongation was due to high ammonium nitrogen. However, Dr. Paul Nelson from the Department of Horticultural Science, North Carolina State University demonstrated in 2002 that phosphorus, not ammonium nitrogen, was responsible for the promotion in stem elongation. To quote: “low phosphate levels result in compact plants, while high phosphate levels result in tall plants.”[1]


This finding has been supported in previous research that shows one of the characteristics of plants grown with low phosphorus is that root growth gains at the expense of shoot growth. Shoot growth is therefore restrained and root activity strengthened. In a study by Danish researchers (2000) with chrysanthemum and potted miniature roses, low phosphorus was found to have a strong growth-retarding effect on stems. Plant height was reduced, with little or no influence on flowering, and there was no impairment of plant quality. The preliminary results of this study indicated a growth-retarding effect in all the tested plant species when the phosphorus levels were at least 20 times reduced compared to a traditionally high phosphorus level. In some species, growth regulation is so effective that it might be possible to replace chemical PGRs in some plant species completely with low phosphorus application.”[2]


How Much Phosphorus in Solution to Reduce Stretch?


Running 20ppm of elemental phosphorus (P) in solution with run-to-waste (RTW/DTW) growing systems during the stretch cycle has been shown to reduce stretch and stack nodes when compared to higher amounts of P (>20ppm). Keep in mind that this is elemental P and not P as P2O5. That is P2O5 is only 43% elemental P; therefore, 20ppm of elemental P is 46.ppm P as P2O5.


Further, it is important to note (a word of warning) that where recycling systems are concerned optimal phosphorus (P) ppm in solution may/will differ due to the preferential uptake of phosphorous by plants at relatively high levels.


That is, in RTW/DTW growing systems fresh nutrient is delivered to the plants at each and every feed. Therefore, if we were to have 20 ppm of P in solution each plant in the RTW/DTW system would receive 20ppm of P at each and every feed.


This situation does not apply to recycling systems where nutrient tank/reservoir practices differ amongst growers. That is, phosphorus is preferentially taken up by plants at relatively high levels. If the phosphorus removed from the nutrient by the plants is not replaced daily in solution at the same levels a P deficiency may occur over several days. For example, to dumb this down a bit, let’s say that we start with 20ppm of phosphorus in solution in a recycling system and the plants in total remove 10 ppm of P per day from this solution. Let’s also say, for this example, the nutrient tank is just topped up with water (no additional nutrients) daily to replace (top up) the volume of solution that the plants remove from the nutrient tank/reservoir every day. Therefore, on day one we would begin with 20ppm of P in solution; on day two we would begin with 10ppm of P in solution; on day 3 we would begin with 0ppm of P in solution and so on. Within three days, under these conditions, the plants are being starved of phosphorus. As such, while reducing phosphorus levels to reduce stretch is an ideal tool for RTW/DTW growers it may be best avoided by recycling growers.


One Other Issue Also Presents  


A problem presents with achieving 20ppm of P in solution in RTW/DTW systems and that is standard off the shelf hydroponic nutrients in many instances contain too much phosphorus to achieve the sort after value, while maintaining optimal EC. For example, based on lab analysis of a U.S. Canna Coco nutrient sample diluted at 2ml/L in RO water to achieve 1.21 EC there is 39. 85ppm P – or nearly two times that of the sort after phosphorus in solution. See following lab analysis.



Looking at the Canna Coco nutrient lab analysis above you can see 39.85ppm of elemental phosphorus is in solution at an EC of 1.12. What this really means is that in order to achieve 20ppm of phosphorus in solution one would need to dilute Canna Coco at 1ml/L, which would then give you an EC of about 0.5 – 0.6 in RO water. This presents as a problem because substrate salinity (EC) is critical where stem elongation is concerned and reducing EC below optimal is shown to increase stretch, while increased EC (salinity) is shown to reduce stretch.[3]  Therefore, an EC of 0.5 – 0.6 is too low for the stretch cycle and ideally your EC, during stretch, should be at about 1.2 – 1.4.


What this means is that while maintaining low phosphorus in solution is a means to reduce stretch, this system/technique may only be suitable for those that formulate nutrients themselves.


Paul V. Nelson, Chen-Young Song, and Jin-Sheng Huang (2002) What Really Causes Stretch? Retrieved from see also, Plaster, E. J (2008) Soil Science and Management pp. 266

[2] Hansen C. W. and Kai N. L, Non-Chemical Growth Regulation of Ornamental Plants. Department of Ornamentals, Aarslev, Denmark, found in Gron Viden Special Issue published in English No. 121 April 2000

[3] Oki, L.R. and Lieth, J.H. Effect of changes in substrate salinity on the elongation of Rosa hybrida L. ‘Kardinal’ stems. Scientia horticulturae; 2004 May 3, v. 101, issues 1-2

Author’s note: I’d like to thank DizzleKush and other members of the community for their invaluable input into this piece. Debates on forums across the globe have been ongoing, re PGRs, and these have provided important stimulus as to what needs to be discussed. Best to all and thanks for the support…. Go safe! Glow

Read the Original Story that Exposed PGRs – The Curious Case of the Flower Dragon by G.Low. (first published on in 2010)

Read more about pesticide use and cannabis …. here
Read about heavy metal contaminants in cannabis…. here

Relevant Links (The Dangers of Plant Growth Regulators) (Are Dangerous Plant Growth Regulators In Your Weed) (Americans for Safe Access. Long Banned Alar (Daminozide) Shows Up on Hydroponic Store Shelves Before Being Removed Again) (Where it all began. The history of PGRs in the hydro market and more)