Modular Hydroponics

Modular growing arrangements make sense indoors. At one time or another just about every indoor grower has seen the benefit of being able to move around an actively growing plant, which includes: maximizing floor space (aisles can be created by simply moving containers out of the way), maximizing artificial light coverage (shorter plants closer to light source), experimentation (different nutrient regimens in separate containers), isolation (diseases, pests and maladjusted plants) and cultural practices which may include flushing, spraying, etc. Now this is usually not a problem when container growing in soilless mix or soil (potted plants). Well how about with hydroponics? Sure, you can wheel around trays but it's not easy to do in a limited space, and individual plants remain stationary (the tall one is still blocking three shorter ones).

One of the most versatile systems to date are modular "bucket" type systems. Many growers are somewhat familiar with this style of system, but we are going to look at some modifications and refinements to help overcome a few of the glitches associated with earlier systems. This type of system can be constructed by the grower with relatively easy to source components and parts. Alternatively, there are some very high-quality manufactured systems that are ready to fill and plug-in. There are endless configurations for setting up individual pods and their proximity to a controller or "heart" unit, which functions similar to a reservoir. Modular bucket systems can be broken down into two distinct classes: drain-to-waste and re-circulating.

Drain-to-waste systems are often the most productive and are generally require less management to operate. However the "drain" part in drain-to-waste means that you have to devise a method in which nutrient run-off is carried away. Many growers make the mistake of just giving the plants enough moisture to wet the medium. Ideally you should have about 20% of the container volume as run-off. This helps to keep the growing medium healthy and reduces the accumulation of salts and nutrients which can impede plant development. For example, if the upper growing container is 2.5 gallons (9.5L), you want to see about 2.5L of (90 Fl. Oz) of run-off if with each irrigation. This is the drawback with drain to waste. You will use more water and fertilizer, combined with the fact that you need a way to channel these large volumes of solution away from the growing area. However, this type of system has advantages over more traditional potted plant irrigation set-ups. While it is true that containerized plants offer mobility, they have open drainage, which means that their surrounding environment is the dumping ground for waste. A bucket system affords the grower mobility while benefiting from the hydroponic aspect of the system. Modular systems can also be configured to retain an amount of nutrient in the lower chamber. In drain-to-waste applications this means that you can maintain a reserve of nutrients in the lower chamber so that in the event of a pump or nutrient delivery system failure, water and nutrient remain available to the roots. In order to do so, the lower chamber must be aerated and vented to prevent disease from occurring as the conditions are warm and the water is quickly depleted of oxygen. This is typically accomplished by means of one or two aquarium airstones continuously aerated by an air pump. Three or more ½" holes are drilled towards the top of the lower chamber, but lower than the inner chamber. The aerating action in the solution reserve will pressurize the lower chamber forcing gases in the root zone to be vented through the ½" openings. This prevents stagnation in the root area and encourages healthy microbial growth, which is an important factor if incorporating organic nutrients and or media.

There are several ways to discharge the spent nutrient solution. Typically, the modules are ground level in order to conserve vertical height. When lamp distance required and container height are calculated you realize that further raising the buckets is not always practical. However to facilitate drainage, insulate against cold floors, and provide leveling squares of rigid styrene set underneath the buckets will also prevent slippage. Root systems sitting against cold concrete floors is typically not favourable unless growing in very warm conditions (including dark cycles).
Usually each module is connected to a drain/return hose ½" to 1-1/4" in diameter by a tee or elbow insert which is fixed towards the bottom of the lower container with a rubber grommet or thru-hull fitting. Rubber grommets are less expensive and can be inserted lower in the outer container as they do not have the flange diameter relative to fitting size as compared to a thruhull. The drain/return hose then finally leads to a large tray sitting slightly below or level to the height at which the drain/return assemblies are connected to the modules. A condensate removal pump is activated by a built-in float switch. When solution is applied to the modules by the feeder reservoir, it passes through the root system and growing media, is displaced in the lower module into the drain/return line, and flows into the return tray. When the level of solution in the return tray rises, the condensate removal pump is activated by the float switch and will pump the used solution through a hose which can be directed to drain or feed outdoor soil gardens. The spent solution can be applied to house plants, trees, and shrubs.

Basically, in re-circulating systems there are two set-ups for nutrient solution storage and delivery. For gardens with fewer lights, or where you want to experiment with different solutions, or have plants in several stages of growth, or an irregularly shaped growing area you will want to install the modules ground-level. In larger scale, more linear (straight-line) set-ups the containers will need to be elevated above the reservoir to some degree, to facilitate drainage.

In floor level applications with central "heart(s)" or controller units, it is critical that the floor is truly level. Otherwise, some modules will hold a greater volume of nutrient solution and may not drain or flow properly back to the controller unit which can lead to serious problems. It is also interesting to note that the concentration of nutrients in each of the containers will remain near equal, even when a few plants are feeding heavier than the majority of the crop (even without the pump circulating). This occurs because the nutrients are diffused throughout the individual modules by the process of reverse osmosis. If the solution concentration is higher in the controller unit than in a surrounding module, the more concentrated solution will be drawn through the tubing to the weaker solution until they are of near equal concentration. This allows you to add nutrients to the central controller for dispersement to surrounding controllers even without the use of a circulation pump. Circulation pumps increase aeration, help lower salt build-up, and rapidly mix and distribute nutrients. However as a failsafe and or for the budget minded, you can produce healthy crops by simply maintaining an airstone in each of the modules. If using only airstones the solution level will need to be maintained to the depth of the roots when transplanted. As the roots descend from the container, the solution level can be lowered accordingly. In situations where circulation pumps are not used, it's hard to buy an airpump that is too large. If shopping for industrial airpumps, always purchase oilless models. You don't want contaminants such as machine oils making their way into the nutrient solution. Some relatively inexpensive dual diaphragm pumps push out up to 25L of air per minute! It is easy to see the difference in the performance of a garden with high levels of oxygen at the roots. If you don't use a high quality hydroponic nutrient with good quality chelates, the aerating action may oxidize plant available minerals to insoluble oxides, inducing a deficiency (iron oxide for example). Additions of premium quality fulvic acids will help hold fertilizer molecules in stable forms that can be absorbed by plants.

With either active or passive nutrient delivery, a constant level of nutrients, water, and dissolved oxygen will be supplied to each of the modules in the set up. A float valve helps to maintain these levels. The float valve is fixed to the central "heart" or controller module. If the system has active nutrient delivery, the controller unit houses both the pump and the float valve. Since all modules are connected to the heart (assuming the surface is level) a decrease of nutrients or water in the system can be observed and modified from this location. So, if the solution level drops in the controller unit as water and nutrients are consumed by the plants in the system, the float valve is lowered and a valve connected to a fresh water supply via tubing allows fresh water or a mild nutrient solution to flow into the controller unit where it is dispersed throughout the system until all modules are more or less equal again.

The general rule of thumb for reservoirs maintained by a float valve with fresh water cisterns, is to allow about half the volume of the nutrient solution in the system to be replaced by the cistern and float valve with fresh, pH adjusted water before draining the entire system and replacing nutrients. For example if you have 10 modules and each module holds a reserve of 2 gallons and the controller unit holds an additional 20 gallons, you will be maintaining a solution volume of 40 gallons. So, if you install a cistern with a capacity of 20 gallons you will know it is time to empty the system and start fresh, as the 20 gallon reserve of fresh water will have been depleted with the float valve maintaining a constant solution depth in the system. Alternatively, instead of topping up with fresh pH adjusted water, the cistern may contain 1/4X strength nutrient solution or a specialty stock solution. Avoid topping up the system with full strength nutrient solutions. Remember that the plants are theoretically consuming 99% water and only 1% fertilizer. You would slowly be increasing the solution concentration to dangerous levels, and the ionic imbalance will force the pH out of the desirable range.

Research performed by several independent growers has demonstrated that gradients (differences in nutrient solution) may develop in level-ground systems, particularly if individual pods are spaced further than two units from a central pod or heart.

In larger scale systems, it may not be practical to use a level ground lay-out, usually because maintaining dozens of controller modules isn't practical and the initial investment can be high. Keep in mind that you will be sacrificing some vertical height because the modules will need to be elevated above the reservoir to facilitate drainage. However, if you set up the garden on an upper floor of a building and maintain the reservoir on the lower floor, you can avoid this problem. Aside from maintaining the amount of vertical height you can allocate to a plant, the nutrient solution can be kept cooler, and you can achieve massive aeration with the height that the water needs to fall down a pipe to reach the reservoir in the floor beneath the garden.
When operating a bucket type system elevated above ground level, the level of nutrient maintained in each module is commonly much lower than levels maintained in a level-floor layout. This is usually a matter of practicality, especially since this type of set-up is better suited to larger scale requirements. Note however, that by maintaining a significant depth of solution at each module you are helping to insulate the plant from temperature extremes, and that the plants will grow rapidly, even in the event of pump failure, as long as airstones are maintained. In raised module set-ups, the thruhull or rubber grommet for the insert to connect the unit to the drain line is installed through the bottom of the bucket instead of lower on the outside of the container. This allows the right angle and tee inserts to be made from the bottom. In this arrangement, the depth of the solution can be maintained in each module by improvising an adjustable overflow tube. This is accomplished by inserting the appropriate length of tubing through the rubber grommet or into the thruhull. Keep in mind that when it comes time to completely drain the system, the overflow tube will need to be lowered in each container to effectively remove all of the used solution. To save time, you may also install a second drain into each module that is level to the bottom of the container. When it comes time to drain the system, simply open a valve that connects to all the bottom level drains in each of the modules. If connected to a pump, this same line can also be used as a nutrient supply line, as an alternative to dripper systems. Essentially this creates a modular deep water flow system (prized by researchers). In either lay-out where the modules are elevated, and the drain is directly on the bottom of the lower chamber, guarding against clogs in the system is essentially. This type of arrangement drains more freely than level-ground systems. However, in doing so, you are more likely to suck a loose rock into the drain tubing causing clogs and overflows. Also, as plants near maturity they will have developed a large root system. A good portion of the roots tend to establish themselves below and outside of the container holding the media. These roots may clog your drain system. Make sure that your growing media (particularly in the case of grow rocks) doesn't fall out of the upper container into the lower container, causing clogs in drain lines. If rotating your plants to maximize light, lift the upper chamber holding the plant and medium instead of just spinning it in place. This may help to lift roots out of drain ports, and will stop you from twisting the root system around and possibly damaging it. An inverted "U" shaped fitting inserted into the drain port will maintain a depth of solution while preventing clogs.

Upper and lower chambers- if constructing your own, the most common materials used are a 3 gallon bucket (drilled with drainage holes) for the upper chamber which sits in a 5 gallon bucket acting as the lower chamber(plumbed for drainage). Buckets should be inert, opaque and food grade. Black are the most commonly available opaque (does not allow light in) containers. Unfortunately, these tend to trap heat and may contribute to overheating of the nutrient solution. If the containers are not 100% opaque, you can cover them with aluminum foil or black and white poly. Some manufactured systems use beige food grade pails which don't absorb heat as readily and are pleasing to the eye; this can be important if you intend to display the system on the patio, etc. Also, if wrapping your containers with an opaque covering you will need to be thorough, as even a crack may let in enough light to harm roots. It also means that you will likely need to re-wrap all your modules after sterilizing between crops.

Drain Assembly & Connection-each module will need to be outfitted with at least one drain. In a level ground system, this will connect each pod to the controller unit. In elevated systems, this will return the solution back to the reservoir, so that it may be re-distributed to each of the modules. In drain to waste systems, this will distribute the nutrient run-off to a sump or return tray so that it may be pumped to disposal (or straight down a drain). Thrhull fittings are used in the marine industry and are well suited for making pipe connections to containers and trays used in hydroponics. Pipe diameter connections ranging from ½" to 1-1/2" are available. Larger diameters are more expensive, and will not sit as low in a bucket as rubber grommets, but are sturdy, leak resistant, and facilitate rapid drainage. Rubber grommets are available in a range of sizes from ¼" to 1-1/2" diameters. They are less expensive, easier to install, require no additional sealant or gaskets, and can be installed lower in the buckets for more complete drainage. If the drain port is installed directly on the bottom (as opposed to lower down on the sides), an inverted "U" shaped fitting will help to prevent roots, growing media, and debris, from blocking the return line. Note that larger diameters are usually less susceptible to clogs.

Reservoir or Controller Module- this is literally the "heart" of the system, much like your own ticker used to distribute nutrients and oxygen in your own system. If using elevated containers that more or less drain completely when in operation, the reservoir will need to hold a minimum solution allowance of 2 gallons per unit. More is better when it comes to reservoirs. If maintaining a depth of solution in elevated containers, the reservoir should have an allowance for 2 gallons of nutrient per module PLUS the volume of solution that will be held in each container. This means that after you fill the reservoir and distribute nutrients to the system after it has drained completely about half the reservoir volume will be stored in the modules. So, even when your system is completely full, the reservoir will look only half full. However, when you open the drain valve to empty each of the modules you will be very thankful that your tank can accommodate all that solution!
In the case of ground-level systems, usually one controller module ("heart")for every four to eight modules containing plants will be centrally located in the pod arrangement to act as the "heart". This module will not contain any plants (for easy access), and will house a float valve (to maintain solution level in the system), and circulation pump (may or may not be present). If growing in high temperature conditions, a stainless steel cooling-coil may be installed in the controller or reservoir to maintain optimal nutrient solution temperatures. For the budget minded, copper tubing can be used for cooling, provided that it has been thoroughly coated with epoxy to prevent metals from leaching into solution, which can become toxifying.

Nutrient Delivery-a circulation pump is most commonly used for distributing, mixing, and aerating the solution. However, in level ground applications, it may not be required if using a high-output airpump with airstones in each module. In this instance, there are no delivery lines to clog, making this a great option for those who want to use organic nutrient solutions in a hydroponic system ("bioponics). In the case of circulation pumps, the nutrient is usually delivered to each of the modules by a spaghetti line (1/4" diameter). Each module should be outfitted with two lines. In the event that one of the lines clogs, the second should remain flowing to supply the plant with moisture, dissolved oxygen, and nutrients. Routine checks will make sure that all lines are flowing freely.
A unique method of nutrient delivery in ground-level systems can be found in General Hydroponics "Aqua Farm" and "Power Grower" modules. Each module has the nutrient circulated and aerated by a single 1.5 Watt aquarium airpump. Air from the pump is sent through the airhose to a column submersed below the nutrient solution contained in each module. The air pressure forces a column of solution to rise through the tubing, where it is distributed over and through the growing media by a drip ring. This also provides a high level of aeration. Many modules can be operated by a single dual diaphragm air pump. Imagine no lines to clog, the same amount of moisture in each pod, and the ability to run each module's solution independent of the other units in the configuration. This is definitely worth considering, as the venturi-drip adapters are available separately for the do-it-yourselfer.

Growing Media-in drain-to-waste systems, you can use just about any growing media of your preference. Grow rocks are nice because they are available in a range of sizes and can be re-used for several crops with sterilization (bleach and water is a common sterilant).
In re-circulating systems, grow rocks are preferred, as they drain quickly and hold lots of air around the root system. You are more likely to have problems with fungus gnats in an organic media such as peat than you are with larger sized, inert, clay pellets. However, some recent research performed by independent growers has demonstrated the benefits of incorporating an organic substrate such as coconut coir with grow rocks. This is usually done in a 50 to 50 ratio (coco to rock). The addition of an organic base encourages healthy microbial growth and can help to buffer nutrients and water. Overall crop quality is improved, and in some instances yields have been increased. The media may remain too wet with the addition of coco for continuous circulation, so the solution will need to be top-fed intermittently. In any case there should be continuous aeration in the lower module by an air pump.