Hydroponic Growing Systems
Hydroponic Growing Systems – Overview
While there are many different hydroponic systems available on the world market they all can be broken into three categories. One is the recycling system, the other is the run-to-waste system, and the third is a system such as a wick feeding system.
Firstly we will look at the recycling system; so named because nutrients are fed to the plants and then recycled back into a central reservoir. The same nutrient is then fed to the plants again and again over the course of several days (via set feed times) until the nutrient is eventually dumped and replaced with fresh nutrient.
I’ve chosen several of the commonly available recycling systems that are sold on the world market. My aim here is to provide examples that use different types of feeding methods. Keep in mind here that there are many variations of these systems. There are also other types of systems. This information is simply aimed at providing you with a better understanding of how some of the more commonly used systems work.
Let’s begin with my choice of what I consider the best recycling hydroponic system (note, best ‘recycling system’ because, in fact, my preferred method of growing is run-to-waste/drain-to-waste growing).
Deep Water Culture (DWC)
The deep water culture method, also known as the reservoir method and deepflow hydroponics, is one of the easiest and oldest of all hydroponic growing systems. In 1976, a method of growing lettuce and other leafy vegetables on a floating raft of expanded plastic was developed independently by researchers at the University of Arizona and the University of Pisa in Italy. Termed DWC the system consists of horizontal, rectangular shaped tanks lined with plastic and filled with aerated nutrient solutions. Those developed in Arizona measured 4 m x 70 m, and 30 cm deep. However, many variants of this system have been developed since by hydroponic growing enthusiasts all over the world. For instance, bubble bucket hydroponic growing is just one example of DWC.
The basic principal of DWC is this.
DWC hydroponics works by suspending your plant roots into a nutrient solution that is heavily oxygenated with an air stone or stones. If you simply tried to hang your plant into a nutrient solution without providing oxygen to the roots, the root system would become starved of oxygen and decay and die. Roots absolutely need a high level of oxygen in order to properly process the nutrients and water they require.
Other than this, nutrient and light do not mix (i.e. light + nutrient = algae), so it is important that the DWC system is lightproof to ensure that nutrient is not being exposed to light.
One advantage to DWC systems, when say compared to substrate based systems which are irrigated at e.g. once every hour and a half, is that the roots are in constant contact with the feed solution which reduces the likelihood of a nutrient depletion zone where some nutrients may become exhausted directly at the root interface between feeds. For this reason, when discussing recycling systems, DWC is my preferred growing system, although run-to-waste growing, in my mind, tends to be better again where novice growers are concerned. I go into a lot more detail about run-to-waste growing versus recycling growing in the nutrient science material I cover here…. I highly recommend that all growers read this material so that they can get a better understanding of what is a critical factor when discussing optimizing yields.
Illustration of a Simple DWC (Bubble Bucket) Hydroponic System
Nutrient Film Technique (NFT)
The NFT system consists of gullies where a thin film of nutrient is constantly recycled through them. Plants are placed in these gullies in small cups containing Perlite. The Perlite absorbs the nutrient and as the roots grow they enter the gullies. From here they absorb nutrients, quickly developing larger root systems which form on the base of the gullies.
NFT is a very efficient growing system. Because of the constant nutrient feed it is possible to maintain ideal, constant root zone temperatures. This greatly aids plant growth due to (potential) optimum uptake of nutrients.
The downfall of this system is that NFT channels are relatively narrow and lack the necessary space for large root systems. As the roots fill the space inside the channel they become blocked and the nutrient starts backing up, eventually flooding the gullies. In extreme cases this will lead to oxygen starvation of the root system, i.e. drowning. This is more likely in cases where larger plants are grown in NFT channels.
Because of this, there are NFT systems that have been developed specifically for larger plants. This type of system incorporates a wider channel that, in turn, accommodates a larger root system. (Speak to your supplier about the types of NFT system that are available)
Another (potential) problem associated to NFT is that it lacks the safety features of media based recycling systems. That is, the lack of media and the constant wetting of the plant’s root system can become a problem in areas prone to high ambient air temperatures. This is because the water/nutrient can become too warm (the warmer the water, the less oxygen it can hold), resulting in low oxygen levels that are available to the plant’s root zone. Once the roots are starved of oxygen they can die quite rapidly.
- Continuous flow of nutrient reduces incidence of salt build up
- Constant root zone temperatures help to facilitate optimal plant/nutrient uptake
- Roots are in constant contact with nutrient solution which is beneficial to root zone nutrient status
- No media required, reduces running costs and clean up
- Very good oxygen capacity (based on nutrient temp)
- Ideal for cooler climatic zones.
- Plants need to be stabilized due to lack of media
- Prone to heat problems/lack of oxygen to root zones in hot climatic zones
- Not suitable/ideal for larger plants (great for lettuce and herbs)
See two different NFT systems below
Traditional NFT System
Wide Channel NFT System
In an aeroponics system, a plant is generally placed into a small basket of expanded clay. The basket is then placed into a much larger lightproof tank (surface of basket sitting flush on the lid of the tank). The tank does not contain any growing media. The tank has a series of spray jets that are used to spray a fine mist of nutrient onto the basket and throughout the inside of the tank. The mist keeps the growing media in the basket moist (and feeds the plant/s). As the root system of the plant grows it enters the tank where it hangs freely (in the air environment) and is kept moist by the mist that is emitted from the spray jets. The spray jets, typically, are run 24 hrs a day.
Aeroponics, like NFT, allows the grower to maintain constant root zone temperatures. This can help facilitate explosive growth and, in some instances, earlier finishing times. Again, however, oxygen starvation can be a problem in areas with warmer climates.
* Ideal for cooler climatic zones.
· Same as NFT system
· Same as NFT system
Media Based Hydroponic Systems
Recycling Hydroponic Systems
Hydroponic Satellite System
The Satellite system is the generic term used for a growing system that consists of multiple pots that each (typically) hold one plant. This system can be used with Perlite, Coco coir, Expanded Clay, Rockwool, or any other growing medium. It is both suitable for recycling and run-to-waste systems. Undoubtedly it is the most versatile of all the systems. If you need to add some plants, simply add new pots to the existing system. Need to remove a couple of plants that aren’t quite looking the goods, simply remove their pots from the system; no decaying root matter left in a single system to create problems for the other plants. This versatility gives the satellite system the growing edge over other systems.
Each unit of the satellite system consists of two pots; one of which is placed inside the other leaving a gap for air and water between the pots. The top pot, which holds the medium, has holes drilled in its base to allow the nutrient to run into the lower pot. The lower pot has a runoff pipe which feeds back to the reservoir via 19mm hosing.
Nutrient is fed via a line from the nutrient tank (approx 15 min of feed every 2 hours depending on medium) to the top pot. This then runs through the top pot, into the bottom pot and back to the reservoir via the 19mm line.
The satellite system is ideally suited for larger plants due to its ability to accommodate large root systems.
Very versatile system
Can be adapted to either run-to-waste or recycling methods of growing
Can be used with all growing mediums
Cheap to add extra plant numbers to the system (simply add more pots)
User friendly: growing medium can help preserve the root zones in times of heat
Easy to move plants around due to separate/independent containers
Root zone temps will vary somewhat depending
on media type and feed times.
Below is a schematic of a basic satellite recycling hydroponic system
Hydroponic Flood and Drain System
The flood and drain system is a recycling system that feeds nutrients to the plants from underneath. A Flood and Drain table is set up with two flow regulators, one of which is connected to a pump. The other is set to release the flow of nutrients at 45mm or thereabouts. A reservoir containing water/nutrients sits at one end of the table beneath the flow regulators. A pump in the reservoir feeds water/nutrients upwards into the table. The table floods to a height of approximately 45mm at which point it begins emptying water/nutrients back into the reservoir. When the pump switches off the remaining water/nutrients drains back into the reservoir (via the pump line) completely emptying the table. This feed routine should occur for a total of 15 minutes every 2-3 hours.
Plants are placed in the system in net pots filled with expanded clay. The table itself is at least half filled with clay to ensure the root system has something to grow into. A light proof material is used to cover the entire top of the table. The lightproof material stops light from hitting the growing medium, eliminating the ability for algae to form on top of the medium. Holes are cut in the material to accommodate the net pots. As the roots grow they enter the growing medium (in the table), eventually forming a dense root mat across the bottom of the table.
Typically, less salt build up than many other media based recycling systems due to immersion of the root system during feeds.
Good aeration where drainage occurs quickly (thus drawing air into the root system)
Where low media levels are concerned, overheating of media can occur quite quickly resulting in low oxygen levels in the media. Because the depth of the average F&D table is minimal this can prove problematic in hot conditions. Root rot can occur as a result.
A Basic Flood and Drain Hydroponic System
Run – To – Waste Systems (RTW/DTW)
Run-to-waste (RTW) or drain-to-waste (DTW) is the term used for a hydroponics system where nutrients are not recycled. Run-to- waste systems (typically) use an inert medium that has similar fluid retention rates to that of soil. That is, run-to-waste mediums retain a high degree of moisture for an extended period. Because of this, feeds are smaller and not as frequent as feeds in a recycling system. In the run-to-waste system plants are given a regulated dose of water and nutrient at such a rate that a small amount of the water/nutrient drains from the medium. The excess water and nutrient is then allowed to drain into some form of catchment away from the reservoir. The waste is never fed to the plants again.
Because nutrients are not recycled there are some distinct advantages associated with the run-to-waste system:
• No nutrient exhaustion as plant receives fresh nutrient at every feed.
• PH Stability over and above that of recycling systems.
• EC Stability (in nutrient tank) over and above that of recycling systems.
• Nutrient less prone to bacteria/pathogen buildup.
• Less maintenance.
The run-to-waste system is ideal for larger plants with high uptake needs. Because of the density and fluid retention rates of the medium, the run-to-waste system has security features unmatched by other systems.
• Roots are well insulated from heat.
• Moisture retention in medium will last for days, giving the plant/s protection from pump and pump timer failures. These are very attractive features for experienced growers who know that heat and equipment failures can very easily wipe out a crop.
Compare the recycling satellite system illustration to this illustration (below) and you will see how the recycling system differs from the run-to-waste system.
A Satellite run-to-waste/drain-to-waste System
Libra tray run-to-waste/drain-to-waste system
COCO GROWTH MEDIUM
Coconut Coir is rapidly becoming the medium of choice for run-to-waste enthusiasts.
Coconut coir holds eight to nine times its own weight in water and more air than premium brand rockwools.
In addition to this Coco coir, unlike rockwool, is bio-degradable which makes it perfect for the garden as a mulch.
Beware however, not all Coco coir products are created equal. In fact, most are not suited for use in hydroponics due to high levels of sodium and other impurities. Because of this, where possible, purchase coir that has been presoaked and pre-buffered. Failing this the medium needs to be flushed with large amounts of water to remove sodium. There is more on this subject further on in the book (C ‘Growing Technique’).
COCO COIR NUTRIENTS
Coco coir has a very strong cation exchange ability. This means that the medium can hold and release nutrient elements according to:
• The plant’s needs.
• The prevailing conditions in the medium itself.
Large amounts of potassium are naturally present in coco coir. Potassium competes with Calcium and Magnesium. For this reason, buffering and plant nutrition need to compensate for this.
For this reason there are several nutrients that are specifically formulated with coco coir’s unique characteristics in mind.
By using a nutrient specifically formulated for the coir-based system, you are ensuring that your plants are receiving the best possible nutrition.
You can read a lot more about coir growing and coir science
Different growing techniques will determine the optimum system configuration for the Coco coir system. Smaller plants are best grown in a Libra Tray system with Coir slabs.
Larger plants, because of their larger root systems, will be ideally suited to growing in 15 – 30 litre pots. Even larger plants will require 50 – 100 litre pots. Many growers use a 40% Perlite, 60% Coco coir mix in this system.
In either case either manual or automated watering can take place.
Automated watering is highly recommended as this allows for many smaller feeds rather than one or two larger feeds done by hand.
We will avoid recommending rigid feed regimes because different plants have their own set of unique characteristics. Suffice to say that feeding rates should be determined by the plant. A good way to ensure that the plant is getting what it needs is to allow for approximately 10% runoff from the overall nutrient delivered per feed (these feed rates can be increased to as much as 30% runoff to compensate for the buildup of salts in the media). Let’s say you had 10 pots and you were delivering a litre per day to each pot; in this case you would ideally be getting 500 -1000ml of runoff over the course of the day. That is 10% of a litre = 100ml x 10 = 1000. You may like to increase this to as high as 15% – 20% runoff if you are using tap water with relatively high salt levels.
When you first put the plants in the system it is a good idea to hold back with feed rates. That is, keep the coir somewhat drier than what you would later on in the cycle. This is because it will force the roots to go off looking for food, ensuring that the root system establishes itself well in the early stages of growth. With this in mind you may want to start the feed regime at 60 – 100 ml per plant, per day. Use your discretion. If the plants begin wilting, in all likelihood they are not getting enough water/nutrient.
AUTOMATED IRRIGATION SYSTEM
Automated irrigation of run-to-waste systems generally incorporates a digital timer (which can be set to 1 minute on/off intervals) with at least 6 on and off settings and a high-pressure pump that feeds through high-pressure line onto 30ml per minute drippers. This system ensures absolute control over the amount of water/nutrient that your plants receive.
Another method less commonly used is feeding from a standard water pump through 13ml line onto 4 ml lines with some form of flow regulator. Again, there is the need for a digital timer that allows for 1-minute settings. Using this system you can ideally bring feeds down to between 30 – 50 ml per minute.
Keep in mind here that run-to-waste mediums have high fluid retention rates so several smaller feeds throughout the duration of the day is the go. This is to maintain optimum oxygen/moisture ratio. Flow regulation is therefore critical.
Rockwool is used on a large scale in greenhouses. A growing number of hobby growers are using it also. Rockwool is clean, sterile and very light. The medium itself does not provide any nutrients. As a result, the grower is capable of determining the exact level of nutrients for the plant. This increases the control over the growing process. Rockwool has a good water/oxygen ratio for the roots.
Make holes in the plastic underside of the rockwool slab, ensuring that the lower end’s edge is cut to allow complete drainage. The Libra trays are on an angle to assist drainage. To enable this we allow for a 10mm difference between each side of the stand’s legs. Cut square holes in the plastic on top of the rockwool slab. Soak the slabs prior to use with a nutrient solution (EC: 1.4, pH: 5.3 – 5.5).
The rockwool slabs are placed in a Libra tray with a corrugated base that allows for runoff and airflow. Attach the drainage pipes to the end of the tray. The excess water can now run into an outlet via these pipes. Regularly check to see that the pipes are not blocked and that runoff can flow freely. Three to five 7.5cm propagation blocks can be placed on each rockwool slab where the square holes have been cut. Use three to five rockwool trays per 600 Watt lamp. The watering process for rockwool systems can be easily automated. In the early stages feed amounts should be regular but minimal to ensure a healthy root system. Once the plants begin to thrive increase feed amounts to achieve a desired runoff of 20%.
A drip-emitter is placed near each plant. The drip-emitters are connected to a capillary pipe, which in turn, is connected to a pump. The pump is controlled by an electronic timer that pumps water to the drip-emitters several times a day. The system can be easily expanded and can be made to fit into any growing area.
Wick Feed Systems
E.g. Smart Valve/Autopot System
The Autopot is a hybrid of the run-to-waste system. In reality it is neither a recycling nor run-to- waste system. Instead nutrients are released to the plant/s via a gravity fed valve. Only when the entire amount of nutrient has been used does the valve release more nutrient. Through this system the plant is determining its own feed rates. Because of this there is absolutely no waste.
The key to this system is the Smart Valve. The Smart Valve is basically a float that doesn’t allow fluid through it until the reservoir that the valve is sitting in is completely empty. When this happens the valve reopens and allows more nutrient/water into the area where the pots are sitting. The plants then uptake the nutrient through a capillary action that occurs naturally in the growing medium. This process is called the Damping and Drying Out process.
This method of hydroponics is simplicity in itself.
However, be aware that simplicity is not always the best thing. Our experience with the Autopot has determined several things.
- Autopots do not offer the same level of control that more sophisticated systems will.
- The nutrient in the reservoir can become too warm or too cold due to the lack of nutrient volume (therefore, prone to temperature fluctuations that are determined by air temps). This can cause uptake problems for the plants (too cold), and potential root rot due to oxygen starvation (too warm).
- The roots often grow into the reservoir. Given that the reservoir only holds minimal amounts of nutrient (approx 1/3 ltr) this water is typically not aerated through the use of an air pump and stone. This means that the water/nutrient is not moving (motionless), which can have a negative impact on root health.
- Lack of flushing, due to the wick feeding nature of the system, can result in salt buildup in the media. (Flush water through pots occasionally to compensate for this)
- Young plants, when placed into the system can initially face stress due to unsatisfactory levels of moisture in the media. (To compensate for this, top feed the plants twice a day for the first two weeks. In addition to this, use a root stimulant for the first week.)
On the other hand, this gravity fed system takes away the need for pumps and timers. Disadvantages aside, the Autopot system tends to perform well and is ideally suited towards beginners and those of you who like to keep things as simple as possible.
OK – so we’ve covered a few of the different types of hydroponic systems. Keep in mind that there are other systems also. You may want to further investigate some of the other options yourself.
My personal choice of system is the run-to-waste method of growing. After many years of experimentation with many different systems I have found that run-to-waste provides the types of features that I look for in a growing system . For this reason, my personal recommendation is a thumbs up to a Coco coir run-to-waste system. Further on in the book there is detailed information that outlines how to use this system.
For now, however, that pretty much covers some basic principals about the various types of hydroponic growing systems.
Now let’s briefly compare run-to-waste to recycling systems where nutrient status is concerned. I have long promoted run-to-waste (often referred to RTW or DTW growing dependent on locale) to novice hydroponic gardeners, so let me explain why this is. When discussing hydroponic growing systems this becomes an important area to touch on early. .
In recycling systems the feed solution (water + nutrient) is fed to the plants and reused. During the course of each feed the plants preferentially remove nutrients at differing levels as it passes through their root systems. The nutrient that is not taken up by the plants and/or absorbed by the substrate is then returned to the nutrient tank/reservoir. Therefore, in a recycling system, because some nutrients such as N, P, K are preferentially uptaken by plants at high levels, while others (e.g. Ca, Mg and S) are taken at much lower levels, the nutrient that returns to the tank/reservoir is altered from the feed solution that was initially fed to them. Put simply, preferred nutrients get depleted, while less needed nutrients accumulate in solution. The feed and recycling process is then repeated over and over again and on each occasion (each feed) the nutrient values are further changed as plants preferentially remove nutrients at differing levels and ratios. As a result, after several days of recycling, the solution that was initially placed fresh in the nutrient tank/reservoir can be greatly altered. This can quickly lead to deficiencies in some nutrients and excesses of others. Additionally, the unused nutrient salts can accumulate in the substrate increasing its EC and impacting on growth. As Savvass et al. (2009) found in studies with recycling hydroponic systems, an imbalance in the nutrient solution is generated by excesses of the ions least consumed by the plant (normally SO4–, Ca2+ and Mg2+), which disrupts the balance of the nutrients and often increases the EC to levels that affect growth and yield. 
While these imbalances can be overcome by monitoring and correcting the nutrient solution, this requires implementing practices (e.g. lab analysis of the nutrient solution or individual nutrient species ion monitoring through the use of scientific testing equipment) that are typically not employed by novice hydroponic growers.
In RTW/DTW growing systems nutrient from the reservoir/tank is fed to the plants and the nutrient and water that isn’t taken up by the plants or absorbed by the substrate is not returned to the nutrient tank/reservoir, but instead runs off into a catchment tank/reservoir as waste. This waste is then disposed of and not run through the system again. What this means is that the nutrient being fed to the plants is not altered by plant uptake and then returned to the tank/reservoir. Therefore, nutrient deficiencies and/or excesses are unlikely to occur and any such nutrient excesses or deficiencies in a RTW/DTW system would be a result of adding an imbalanced nutrient or too little or too much nutrient to the tank/reservoir in the first instance. This is just one reason why I promote RTW/DTW growing to novices in Integral Hydroponics. Quite simply, RTW/DTW growing, when handled correctly, promotes a better nutrient status in the root zone than does recycling.
Another issue associated with recycling systems is the potential spread of plant root pathogens, where the presence of just one infected plant will put the entire crop at risk. Oomycetous pathogens in particular, such as Pythium and Phytophthora, can easily spread and propagate explosively under favorable conditions, causing serious damage.
Growing RTW/DTW significantly reduces the risk of root zone pathogen cross contamination between plants. This is because the plants aren’t being fed a recycled nutrient that can become contaminated by a single diseased plant and as a result of then feeding the contaminated nutrient to the rest of the plants infect the entire crop.
One other benefit of growing RTW/DTW is that when compared to recycling systems it reduces the daily nutrient tank maintenance time. For instance, what I do is set up a 200L nutrient tank/reservoir and feed it onto a 100L tank through a float valve system (300Ls in total when a fresh batch of nutrient is made up). This means I can stock up on a lot of nutrient working solution. Because the solution isn’t recycled, EC checks, water top ups, and nutrient dumps aren’t required (although I do check the solution pH every day).
Doesn’t RTW/DTW growing mean using more water and nutrients than in a recycling system?
In short, yes it does. Aside from the advantages RTW/DTW systems provide they have one primary disadvantage when compared to recycling hydroponic systems. They use more water and nutrients. In fact, some countries (e.g. the Netherlands) in order to minimise eco harmful nutrient (e.g. nitrate and phosphate) run-off have introduced regulations that limit the growing of commercial crops in RTW/DTW systems. Therefore, one consideration re RTW/DTW growing is that the waste has to be disposed of carefully. However, keep in mind that regulations limiting RTW/DTW growing were introduced because of the huge-scale of hydroponic production in the Netherlands (100% of many greenhouse crops being produced hydroponically) and the potential cumulative impact that this could have on the environment. Conversely, where small home grows are concerned and where waste is disposed of correctly (e.g. dilute it and use it to lightly fertilize your garden, avoiding run-off into the water table and water ways) environmental concerns don’t present as much of an issue.
One study that compared recycling to RTW/DTW showed the average water and nutrient saving when growing tomato in a recycling system is 24 % water and 34 % nutrient. Inline to this, I find that the RTW/DTW growing methodology I practice tends to use about 30 – 35% more nutrient than ‘DWC’ (Deep Water Culture; e.g. Bubble Buckets), my preferred method of recycling growing. However, when considering the extra nutrient and additive use, this equates to perhaps $30.00 extra worth of consumables per cycle. What you then need to consider is whether this extra $30.00 will be compensated for due to benefits to yields; i.e. will 5-10% extra yield gained through RTW/DTW growing compensate for the $30.00 more spent on nutrients and additives?
 Savvas, D., Sigrimis, N., Chatzieustratiou, E., & Paschalidis, C. (2009). Impact of a progressive Na and Cl accumulation in the root zone on pepper grown in a closed-cycle hydroponic system. Acta Horticulturae, 807, 451-456.
 Tuzel, I.H., Tuzel, Y., Gul, A. Meric, M.K. Yavuz, O. Eltez, R.Z. (2000) Comparison of Open and Closed Systems on Yield, Water and Nutrient Consumption and Their Environmental Impact