ABSTRACT
Most hydroponic systems are adaptable to small-scale backyard greenhouses� However, not all are practical� The choice also depends upon the crop grown� Lettuce, arugula, bok choy, basil, and some herbs do best in a nutrient film technique (NFT) or raft culture system� Vine crops prefer pots or slabs of perlite, coco coir, rockwool, or mixtures of these substrates� To increase the production of lowprofile herbs, bok choy, and strawberries, plant towers are the preferred system using peat, perlite, coco coir, or mixtures of these media� Usually in a backyard greenhouse, we wish to grow most of these crops together� The first step then is to determine how much of each crop you like in your salads on a weekly or monthly basis� Next, is to decide on the best system to use for each crop and how much area is to be occupied in the greenhouse by each with its hydroponic system� Finally, make a detailed plan of the location of each crop in the greenhouse and the specific area occupied by each one�
Hobby greenhouses come in many dimensions as was described in Chapter 19� The width limits the number of plant rows or beds that it can contain� Greenhouses of 8-ft width will fit two beds, and 10-12-ft wide greenhouses have three beds� The center of the greenhouse is 9-ft to 10-ft high from the base� If the structure has the base (sills) set on a concrete block foundation, the height may be raised several more feet� This extra height helps greatly to accommodate tall vine crops� Locate European cucumbers, peppers, and eggplants in the center bed of the greenhouse where the height is greatest, as these plants are difficult to lower� Tomatoes can be located on one of the side beds and low-profile plants and plant towers on the other side and as shown in the crop plan of the last chapter (Figure 19�27)�
Pre-wrapped rockwool and coco coir slabs are available at hydroponic shops or online� They come in widths of 6″, 8″, and 12″ by 3″ thick by 3 ft long� They cost $6-7 each� I highly recommend purchasing these slabs instead of making them from polyethylene� Especially the coco coir slabs as they will be leached to remove any sodium chloride from the substrate� Rockwool slabs are only available as wrapped� The slabs are roughly 3 ft long� Four slabs will make up a 12-ft row to fit in a hobby
greenhouse of 12-ft length� If you wish to grow all vine crops using only slabs, four will fit on each side and three in the center row of the greenhouse� The slabs are perfectly suitable for low-profile plants� Simply make the plant holes at 6″ centers within the slabs and place three rows of slabs (using 6″ wide slabs) 3″ apart to get a 24″ growing bed� The disadvantage of using the slabs instead of raft or NFT for lowprofile plants is the high cost of the slabs� To obtain a growing area of 2 ft wide by 9 ft long a total of 3 × 3 = 9 slabs would be needed� The cost would be approximately $60� In addition, it is difficult to re-use the slabs for more than two to three crops as they may become contaminated and/or get damaged physically during the harvesting of the plants� That would result in replacing the slabs 5-6 times a year so the cost could escalate to $300-350 annually� For these reasons, stay with the conventional methods of growing specific crops�
For tomatoes, peppers, and eggplants locate three plants per slab (Figure 20�1)� That is 12 plants per row of four slabs� Space the plants within a slab at 6″ from each end with one in the middle� For European cucumbers transplant two plants per slab, one at 9″ from each end of the slab and space the slabs 6″ apart end-toend� Then, in a 12-ft row there would be three slabs instead of four slabs as with the tomatoes, peppers, or eggplants� That would give six cucumber plants per row�
The slabs are set on top of a 1-2″ thick Styrofoam sheet to insulate the roots from the cold floor of the greenhouse (Figure 20�2)� Alternatively, construct raised beds to set them on, but that will take away from the overall height to train the plants� Cover the Styrofoam insulation with black polyethylene plastic to permit drainage
to occur over the sides of the Styrofoam to minimize the growth of algae� This is an open system as shown in the diagram� To construct a re-circulation system to collect the leachate and return it to the cistern tank, use rigid plastic channels� These channels are available from hydroponic shops or online� Place the channel on top of the Styrofoam insulation, sloping it about 4% back to the cistern�
You could also construct beds from plywood and a steel-frame� Make low beds to get a slope of 3% back to the cistern� That is a 4-5″ slope back to the top of the cistern� The bed would be 6″ high at the entrance end of the plant row sloping to the cistern having 2″ of freeboard (above ground level)� Make the bed with 2″ sides using 1″ × 2″ lumber� Construct the width 2″ wider than the slab width� Using 8″ wide slabs make the width of the bed 10″ (inside width)� Cut the Styrofoam the same width as the slabs as they will sit directly on top of the Styrofoam� Staple 6-mil thick black polyethylene at the top edge of one side of the bed, bring it over the Styrofoam and push it between the Styrofoam and the other edge of the bed to form a channel where the leachate can run along and enter the cistern at the lower end as shown in Figure 13�22� Staple the other side of the black polyethylene liner to the upper edge of the bed side�
Bato buckets are special pots designed in Holland for coarse media such as perlite, expanded clay rocks, or pea gravel� With these coarse substrates, the bato bucket maintains about 2″ of solution at the bottom� This level of solution is regulated by a siphon pipe� The bato buckets sit on top of a 1½″ diameter PVC drain pipe� Holes of 1″ diameter are drilled into the top of the drain pipe to fit the siphon elbow from the base of the bato bucket� The holes are spaced at 16″ centers along the drain pipe� Begin the first hole about 8″ from the end of the drain pipe to allow a cap at the end
of the drain pipe� Do not glue the cap as that is access to clean out the drain pipe� The drain pipe lies on the greenhouse floor with a very slight slope back to the cistern by adding some pea gravel under the pipe and pots� Bato buckets cost about $6�50 each and can be re-used between crops for at least 5 years� Clean them between crops with a 10% bleach solution by soaking them for 1 h or slightly longer�
Eight bato buckets in 10-12 ft will give adequate plant spacing (Figure 19�27)� Each bucket will hold one European cucumber or two of tomatoes, peppers, or eggplants� Usually it is better to plant one eggplant per bucket as eggplants have large leaves that intercept more light than tomatoes or peppers� Other low-profile crops such as herbs, lettuce, arugula, basil, bok choy, cabbage, cauliflower, broccoli, green onions, bush beans, and many more can be grown in bato buckets� Between crops simply sterilize the pots and replace new substrate� They are more economical than slabs to grow these crops since only the substrate needs replacement between cropping cycles� Herbs, of course, can be harvested for up to 10 months, depending upon the herb’s growth cycle� Even strawberries would grow in bato buckets� During the hot weather seasons from late spring to early fall, grow cool-season crops such as cabbage, cauliflower, and broccoli outside in your soil garden as the greenhouse would be too hot for them at that time of the year�
Plant towers increase the number of plants that can be grown in a unit area of the greenhouse compared to ground-level beds� Usually, at least 6 times the production is achieved in plant towers compared to ground beds� Other advantages include easy maintenance and harvesting of the plants, clean product as the crop is above the ground level, and the solution can be re-cycled� The dimensions of the Styrofoam pots for the plant towers are 9″ × 9″ × 8″ tall� Each pot is specially designed so that the pots sit one on top of the other without nesting by fitting their bases into four cuts in the lip of the pot below� This is a patent design� The pots are sold by Verti-Gro, Inc� in Florida (see Appendix) at a price of $4�50 each� They will easily last 5 years� The bottom pot should sit on top of a collection pot that returns the solution back to the cistern via a 1½″ drain pipe� Stack up to seven pots or more depending upon the greenhouse roof height� A galvanized electrician’s conduit with a 1″ diameter PVC sleeve supports the pots vertically� Secure a support cable on the ribs of the greenhouse centered directly above the row of plant towers� The conduit is attached to the cable to keep the plant towers vertical� The remaining details of setting up the plant towers were given in Chapter 13, on “Plant Towers” including Figures 13�26 and 13�27� For only two plant towers as in Figure 19�27 of the greenhouse crop layout, let the plant towers drain to waste�
Plant towers are best for herbs, bok choy, and flowers such as marigolds, nasturtiums, viola, petunias, and all hanging-basket type of flowers� Do not use them for lettuce as harvesting often and changing the plants is a lot of work, nonetheless, the towers will produce very nice lettuce� Do not grow any vine-crops or even bush-type tomatoes, peppers, eggplants, and so on as these plants cast a lot of shade on the ones immediately underneath causing very poor yields in the lower plants� A detailed description of the irrigation system follows under that section of this chapter�
This hydroponic system is best for lettuce, basil, arugula, and some herbs� It can easily be set up in a backyard greenhouse� In our example, a raft system could occupy the bed area along one side or in the center as a full bed length or a portion of it� The first step is to decide on how many lettuce, basil, arugula, and some herbs are eaten weekly� From this extrapolate, the area of raft culture needed to fulfill your requirements assuming the cropping cycle for these plants is about 6 weeks� Spacing of these plants is 6″ × 6″ so you will get four plants per square foot of the bed surface area� As shown earlier in the plant layout (Figure 19�27), 48 plants will fit in a bed 2 ft wide by 6 ft long� The raft system is self-contained so its operation is independent of the other hydroponic systems in the greenhouse� It will have an air pump above the bed that circulates air by a poly hose to air stones in the pond� Locate the air pump above the top level of the pond in case it should stop and thus not allow solution to flow back to the pump� These components and supplies are available from an aquarium store or Aquatic Eco-Systems, Inc� in Florida (see Appendix)�
In northerly climates with cold soils, especially during the winter months, low temperatures will chill the nutrient solution below optimum of the raft system, which is about 65-68°F� Even in the greenhouse with a weed mat and gravel base as described in the preparation of the site for the greenhouse in Chapter 19, the cold will affect the temperature of the nutrient solution� For this reason, place a 2″ thick Styrofoam board under the area where the raft pond is to be built� During long-term cold periods, the solution may have to be heated with an immersion heater�
Construct the sides of the pond with 2″ × 10″ treated lumber� Set these sides on top of the Styrofoam� In constructing one of the side beds of the greenhouse, make the inside dimensions 48½ wide by a length 4″ less than the inside length of the greenhouse� When cutting the Styrofoam boards (rafts) allow at least ½″ play (less length than the inside length of the bed)� Screw the lumber together with stainless steel screws and glue the joints� Set the perimeter frame on the Styrofoam and then install a 20-mil swimming pool liner, folding the corners similar to making a parcel followed by nailing the top edge onto the wood frame using a cedar wood lathe or aluminum angle as shown in Figure 13�2�
The Styrofoam boards can be either 2 ft × 4 ft or 4 ft × 4 ft in dimensions� Make the holes for the transplant plugs at 6″ × 6″ spacing starting 3″ from the edge of the boards as shown in Figure 13�4� Each 4 ft × 4 ft board should hold 64 lettuce, arugula, or basil plants� It is easier to handle 2 ft × 4 ft boards especially when harvesting as the plants weigh up to 6-8 ounces or more each� With fewer plants, it is unlikely that the boards will break from the weight as occurs with 4 ft × 4 ft boards�
This system was discussed in Chapter 13� Several types of these systems are available commercially on the Internet or at hydroponic shops (see Appendix)� Some of the systems use a substrate such as expanded clay aggregate, coco coir, perlite, granular rockwool, and mixtures of coco coir, perlite, and rice hulls combined at different ratios� The expanded clay aggregate gives best drainage, is inert and pH neutral� It
is re-usable by cleaning and sterilizing it between crops using a 10% bleach solution or hydrogen peroxide followed by rinsing� However, with subsequent cropping roots may enter into the clay particles and make it difficult to sterilize� This substrate can easily be replaced with new between crops�
Most of the ebb and flow systems use 5-gal buckets or some form of growing pots of that volume� The pots have a felt or screen liner bag that contains the substrate to prevent clogging of the drain outlet as particles may come off the substrate with continued irrigation and drainage cycles during the cropping period�
The components of the system include a large nutrient solution reservoir of 50 gallons or larger� A submersible pump operated by a time-clock that pumps water from the storage tank to a smaller distribution reservoir of about 5-10 gal is shown in Figure 20�3� The inlet line is attached to a float valve (also acts as a safety backup) that regulates the inflow of solution to the distribution tank� From the distribution tank, a ½″ black poly tubing connects to each grow pot� As the solution flows to the distribution tank, it also flows by gravity to each grow pot filling it from the bottom� There are basically two systems, one the fill-up system and the other the drainage system (Figure 20�4)� During the fill cycle, a timer activates the pump in the large reservoir and the solution flows to the distribution tank� On the return cycle, a second time-clock activates the pump in the distribution tank to pump the solution back to the main reservoir as the first timer shuts off the pumping cycle to the distribution tank� The two timers are synchronized so that as one is operating the other is off� The solution flows back from the grow pots to the distribution tank where it is pumped back to the solution reservoir� A second float switch on the bottom of the distribution tank will sense when the growing pots are empty to stop the drain pump from operating even if the return cycle timer is still activated� Ebb and flow cycles are timed according to the plant water needs� The fill and drain cycle levels may be regulated by electronic sensor switches that operate the pumps via a controller� This system was also discussed earlier in Chapter 13�
An option to this ebb and flow system is to use a top feed drip irrigation system� The grow pots are set up similar to the ebb and flow system with a drain tube connecting each pot to the distribution tank� Two float valves or electronic switches, one at the lower limit and the other at a high limit will operate the submersible pump that conducts the solution back to the nutrient reservoir as it returns from the grow pots� The difference in this system is that the submersible pump in the main solution reservoir irrigates the grow pots directly by a drip irrigation system rather than pumping to the distribution tank�
The system may be set up as a closed system whereby the returning solution is collected and conducted back to the distribution reservoir where it is pumped back to the main reservoir� Otherwise, with an open system there would not be a return
drain line to a distribution reservoir, the leachate would drain to waste through the greenhouse floor�
Ebb and flow systems are available that use no substrate making them more of a water culture system (see Current Culture H2O in Appendix)� The principles of operation are very similar to the one just described, but without a medium, growing the plants in an 8″ net pot that is irrigated from below� Nonetheless, even with this system it would be better to use expanded clay in the net pots� In that way, the transplants are kept higher in the pots so that their crowns are above the upper water level at all times�
A drip irrigation system is the basis of most hydroponic cultures� The specific cultures including coco coir, expandable clay, peatlite, perlite, rice hulls, rockwool, sand, sawdust, and various mixtures of these all use drip irrigation� The various cultures may be named by the substrate used, but overall they are all drip irrigation systems� While most commercial drip irrigation systems use an injector/proportioner component, in backyard greenhouses it is more economical to use a nutrient tank of normal strength solution than stock tanks of concentrated solution that is diluted by the injector� The drip system may be an open to waste or a re-circulation design� I recommend using a closed (re-circulation) system to prevent the solution from draining directly below the greenhouse, which may cause a moisture build-up, especially in northern climates during the winter months� When you change the nutrient solution it may be pumped to your garden and landscape plants, especially when those plants are actively growing�
The first component is a nutrient reservoir� In a backyard greenhouse with the peak being relatively low at about 9 ft, it is better to keep the plant growing systems at floor level� Locate the nutrient reservoir at the end of the greenhouse opposite the entrance door� Set the reservoir into the ground so that the top is 2″ above the floor of the greenhouse (Figure 20�5)� Purchase a plastic tank of approximately 200-250 gal in volume, but it must not be a tall tank to facilitate burying it� Additionally, if the greenhouse is located in an area of high groundwater table, it could cause the tank to collapse� A more ideal tank is a rectangular one of about 18-20″ wide by 2 ft deep by 8-9 ft long� If you cannot locate such a tank, use a number of plastic storage tanks and join them by bulk-head fittings at the bottom of the sides� In that way, the modular tanks will in effect be one� Place 2″ thick Styrofoam on the bottom and around the sides of the excavated area between the soil and the tank to insulate it from the cold soil during winter months� Construct a cover of ¾″-thick plywood� Seal it with oil-based paint�
The rest of the system includes a pump, time-clock controller, piping, and the drip lines as shown in the diagrams (Figures 19�28 and 20�5)� Use a submersible fountain pump or a sump pump operated by a controller� The volume (gpm) of the pump is calculated by the number of drip lines, which is a function of the number of plants� In our example hobby greenhouse, if we grew all of the plants in slabs or bato buckets the maximum number of vine crops the greenhouse could contain would be three beds with 12 plants each for a total of 36 plants� If each plant receives one drip line on an emitter of 0�5 gal per hour (gph), the total flow would be 36 × 0�5 = 18 gal per
hour� Select a pump that has a flow capacity of twice that for lots of flexibility in crops, which would be about 40 gph� The next step in the pump selection is the lift it must satisfy� This is done by calculating the total frictional loss within the piping� These calculations are not presented as for such a small greenhouse a lift of 10-15 ft would be more than adequate� Finally, the pressure should be about 30 lbs per square inch (psi) to enable the operation of solenoid valves if you should wish to irrigate some of the rows with different cycles and periods of watering� This applies to the growing of numerous crops having different water demands� If this flexibility is preferred, a controller having 4-5 stations would have to replace the simple time-clock� I do not recommend this type of sophistication for a small backyard greenhouse�
To select the best value of pump with a low flow rate of 40 gph, the lift is inadequate due to its very small size� I prefer to select a larger pump and install a bypass line back to the solution reservoir to regulate the flow volume� There are small fountain pumps of 800 gph capacity with a lift of 12 ft for less than $50� These types of pumps would not produce sufficient pressure to operate solenoid valves� There are a number of “Little Giant” submersible pumps with a capacity of 70 gph up to 12 ft of lift with a pressure of 5 psi for about $100� They are 1/40 HP at 100 watts and draw 1�7 amps of electricity� Other models for about $150 have a
capacity of 200 gph at 14 ft with a pressure of 7�5 psi with a ½″ male outlet� They are 1/15 HP at 200 watts and 3�2 amps� For pressure compensating emitters of 2 liters per hour (0�5 gph), a pressure of 14�5 psi is optimal pressure for their operation� However, at 7�5 psi the volume of water delivered is a little less, about 1�75 liters/h or 0�46 gph, so this is an acceptable rate of flow� At lower pressure a larger emitter could be used� For example, a 4 liter/h emitter would give you 3�5 liter/h (0�9 gph) at 7�5 psi or about 3 liter/h (0�8 gph) at 5 psi� Alternatively, the length of any irrigation cycle can be increased when using a lower volume delivery of water by the emitters under lower pressure� In general, it is best to be oversized in the pump and use the bypass to cut back on the flow volume� The maximum pressure for the drip emitters is two bars or 29 psi� At that pressure they will deliver twice the volume that they are rated at as the rating is based upon 1 bar or 14�5 psi of pressure� There are also larger submersible pumps such as the Little Giant onesixth HP utility pump capable of 840 gph at 15 ft of lift� It has a 1″ discharge� It draws 5 amps and uses 380 watts of power� It costs about $150� This size of pump would be a better choice over the smaller models�
Some suitable pedestal sump pumps are available� The advantage of the pedestal sump pump over the submersible types of pumps is that the pump motor is not in the presence of the nutrient solution� Many submersible pumps eventually start to leak and break down due to the corrosive action of the nutrient solution� All impellers of any of these pumps must be either plastic or of stainless steel to resist corrosion� A 1/3 HP pedestal sump pump will deliver up to 2100 gph at 15 ft or 900 gph at 20 ft of lift with 8�65 psi� The electrical demands are 330 watts at just under 3 amps and require a 15 amp circuit� They have a glass reinforced nylon impeller�
Pedestal sump pumps cost between $80 and $100� These types of pumps are available at a building supplier, plumbing store, or online�
The next step is the piping from the pump to a header to which the drip irrigation lines are connected� The connection to the pump depends upon the type of pump and its outflow diameter� The submersible pumps mentioned earlier have ½″ or 1″ outlets� The pedestal pump has a 1¼″ outlet� The ½″ outlet needs a female adapter connection while the others use a male adapter fitting� If using the larger submersible or pedestal pumps install a bypass (Figure 20�5) to regulate the volume flow of the pump as it exceeds that needed for the drip system� Use flexible black polyethylene piping from the pump to a header pipe attached to the back wall of the greenhouse about 30″ above the top cover of the solution reservoir as shown in the diagram� Install a ¾″ diameter bypass line from the pump riser with a union and a gate valve in this line as it returns to the nutrient reservoir� Keep the gate or ball valve near the upper end of the pipe so that it is easy to adjust� Then, with an elbow, make the return to the tank� Immediately before connecting the inlet from the pump to the header install a 100 mesh filter� The header pipe should be 1½″ diameter schedule 40 PVC� Attach the inlet from the pump with a PVC tee� Assuming there are three beds of plants assemble the header with two 1½″ elbows (one on each end) and one 1½″ tee for the middle bed� Install a ¾″ ball valve downstream from the tee or elbows within 2″ of the fittings� The ball valves will allow the balance of flow to the drip lines� After the ball valves convert the piping to black poly from PVC using a slip thread reduced bushing converting from ¾″ to ½″ to adapt to the ½″ black poly drip hose�
Place the drip lateral line hose on top of the bato buckets or at the sides of the slabs� Use a 3″, 1″ diameter piece of PVC pipe to plug the end of the poly hose by bending about 6″ of it back and slipping the PVC piece of pipe over it as a sleeve� Alternatively, you may purchase a Figure “8” end stopper� Make up 18″ long drip lines from 0�160″ to 0�220″ diameter drip line� Punch the holes for the emitters in the poly hose using a special punch tool available from irrigation stores or online� The position of the holes can be on the top of the black poly hose for easy access� Locate them where the plants will be set� Insert the emitters and attach a drip line to each� Insert the other end of the drip line into a barbed stake that will keep the water from spraying on the plants� One stake will be placed on top of the rockwool block in which the transplant is growing�
If plant towers are located in one of the rows bring the ½″ black poly hose from the header up to the top of the plant towers and thread it through a 1″ tee at the top of each plant tower� The tee is fixed to the outer sleeve support of the plant tower as shown earlier in Chapter 13 (Figures 13�26 and 13�27)� From the black poly hose insert three compensating pressure emitters of 4-8 liters/h (1-1�5 gph) above each plant tower� Make two drip lines long enough with sufficient slack to enter the top pot of the plant tower and the other one to reach the center pot of the plant tower� Insert a barbed stake at the end of each drip line to secure it into the substrate of the pot�
The plant towers are set up exactly as explained in Chapter 13 with the exception of the supporting frame dimensions� The plant towers in the greenhouse could drain to waste or the solution could be re-cycled by raising them up on a frame to an elevation above the nutrient tank (about 6″)� The collection pot would conduct the solution to a return pipe going back to the nutrient cistern� In this case, construct the supporting frame to a height of 6″ or slightly higher to enable the spent solution to return to the cistern�
There are many systems to choose from, so select the ones that best suit the growing requirements of your plants� You can easily assemble a number of different hydroponic systems within a backyard greenhouse� Construct all of these systems yourself from components readily available from hydroponic shops and irrigation suppliers� Websites such as that of Grainger, Inc� offer their online catalog that contains heaters, fans, pumps, time-clocks, controllers, and many other components (see Appendix)� Enjoy the fun of building your own systems and experimenting with different ones to determine which crops and systems work best together!
