Sources of Supplies and Components for Backyard Greenhouses

Often supplies and components for backyard greenhouses may be sourced from local building suppliers, distributors for plumbing, electrical, and heating components� For specific greenhouse-related supplies and components contact greenhouse builders and distributors as well as hydroponic outlets� There are specialized manufacturers and distributors of hobby, backyard greenhouses, their components, and supplies� If you are in the market for a backyard greenhouse visit personally some of these companies as they will be able to assist in your decision as to the size, nature, and type of greenhouse most suitable for your needs� They can also recommend the components of heating, cooling, lighting, and so on to provide optimum growing conditions in a specific location� They can calculate the heating and cooling capacities for your area and recommend the size and type of these units to purchase� Consider capital and operational costs of various options of these components� The optimum levels of environmental factors are also a function of the crops grown� Normally, the capacities of the components are based on the extreme levels of the weather conditions� Under such extremes, the conditions within the greenhouse can be maintained at less than optimal, but adequate to prevent any damage to the plants� Extremes generally occur over relatively short periods during the early hours of the morning so will not have long-term effects on the health of the plants�

Control of optimum temperatures is based upon heating and cooling� These two factors are regulated by heaters, ventilation fans, evaporative coolers, and shading (Figure 21�1)� These components are available from many suppliers of backyard greenhouses (see Appendix)�

Smaller greenhouses up to 20 ft in length by 10-12 ft in width may be heated with space heaters� Longer greenhouses should use unit heaters with a convection tube that distributes the heated air rapidly down the length of the greenhouse� The unit heater has a fan at the back that blows the air over heat exchangers into the convection tube� This type of heating system is mounted in the peak area of the greenhouse and circulates heat above the plants� It is not as efficient as using hot water from a boiler through heating pipes at

the base of the plants� But, such a hot-water heating system is very costly although much more efficient in providing more uniform heat throughout the crop and is less expensive to operate� A mixing fan or horizontal air flow (HAF) fan mounted just above the crop assists in mixing the air within the greenhouse� The heating systems discussed here are space heaters as most backyard greenhouses are of 10 ft × 12 ft or 10 ft × 16 ft and such a heating system is efficient and economical for the greenhouse size�

In Chapter 19, heating calculations and some websites that provide such information were presented� Projected costs of heating were also given� Emphasis here is on the types of heaters and their advantages or disadvantages along with cost ranges for the various types and models (Figure 21�2)� Space heaters may be electrical or fired by propane or natural gas� Natural gas from your house would provide the most economical operational source of heat, but, the cost of installation is more expensive than to use propane or electrical sources� An underground cable must connect the greenhouse with the residence, so size it sufficiently to meet the demands of the space heater (usually 220 volts, 30 amps)� A 220-volt heater is more efficient than a 110-volt one and at the same time has more heating capacity� Most of these heaters come with a two-speed fan� The 220-volt heaters, compared to 110-volt ones, have a stronger fan that can better mix the air in the greenhouse�

An alternative is to locate electric baseboard heaters along the sides of the greenhouse� The air will rise up and circulate as it cools� The disadvantage with this type of heat is that it is located very close to the outer rows of plants and could cause burning of leaves of those plants� The heat is focused in one area of the crop and can also reduce relative humidity to low levels near the site of the heaters� If baseboard heaters are installed, a HAF fan should be mounted near the top of the crop above one of the aisles or the center row to mix the air to create convection currents�

Infrared heaters of relatively small sizes are available for application in backyard greenhouses� The advantages of infrared heaters are lower electrical consumption, no noise from a fan, and they heat the plants and you, not the air� There are a number

of types, but all are mounted above the crop to maximize coverage� Some are natural gas or propane operated while others are electrical�

Modine manufactures several natural gas or propane small models of 30,000 and 50,000 BTUH, respectively� In our greenhouse example of 10 ft × 12 ft (see

Chapter 19), for weather conditions of Seattle, WA, the heating system capacity was 9700 BTUH� The Modine heaters would be too large for this size of greenhouse� Other types of infrared heaters are available as a modular design with single, double, or triple emitters (heater units) in one unit� These are electric and a selection of wattage, voltage, and amperage per unit gives versatility in satisfying numerous heating demands� The smallest one emitter is 1�5 KW and 12�5 amps going up to three emitters at 6 KW and 25 amps (240 volt)� They are wall-mounted with special brackets or supported overhead with chains� These heaters may be mounted singly or in banks up to 3 units� The smallest unit (one emitter) mounted at 8 ft will cover a surface area of 10 ft × 10 ft × 12 ft to supply heat over 110 sq ft of surface� The two emitter model, mounted at 10 ft, covers 160 sq ft of surface heat zone� Prices range from $400 for a single emitter to $600 for 4 KW, 19 amp triple-emitter heaters� They are considerably higher in price than standard electric space heaters, but over time the savings in heating costs would compensate for the higher initial capital cost�

The smallest 120-volt electric portable greenhouse heater capable of generating 5120 BTU can heat up to 120 sq ft of greenhouse� It comes with a thermal cut-out to prevent overheating� However, a single-stage thermostat could be wired in line to operate the heater� This size of heater is too small for a 10 ft × 12 ft greenhouse� I have found it is good for an 8 ft × 12 ft free-standing or lean-to greenhouse� This type of heater is available for just under $50� A larger 240-volt, industrial electric heater produces up to 19,000 BTU� It is 5600 watts, 23 amps with a built-in thermostat, and thermal safety limit switch to prevent overheating� This size of heater easily fulfils the heating needs of our 10 ft × 12 ft greenhouse example and would be adequate for a 10 ft × 16 ft greenhouse� It costs about $150�

Natural gas or propane greenhouse heaters will generate from 20,000 to 25,000 BTU� These are suitable for larger backyard greenhouses of at least 10 ft wide by 20 ft long� However, they are also recommended for greenhouses of 150-175 sq ft of floor area in more northerly locations� They are available as vented or nonvented models� If using a nonvented heater the source of natural gas or propane must be clean burning not to create any carbon monoxide or other byproducts that could damage the plants� For this reason, it is safer to use a vented model� All gas-burning models must have a fresh air intake to provide oxygen for complete combustion� A 2-3″ PVC intake pipe mounted within 1 ft of the floor at one side of the heater is recommended� Place an elbow oriented downward on the outside with a screen cover to prevent water and rodents from entering the greenhouse� Prices, based on size, vary from $450 to $600�

The next step in temperature control is ventilation to assist in cooling the greenhouse� Ventilation is achieved through the use of exhaust fans and circulation fans� The size of ventilation fan is determined by the volume of air in the greenhouse to be exchanged once per minute, which is expressed as cubic ft/min (CFM)� CFM is expressed as: CFM = Length × Width × 12� Our example greenhouse has a needed air volume exchange of: 12 × 10 × 12 = 1440 CFM� Select an exhaust fan based upon that air exchange rate� Ventilation packages are available that include a shuttered

exhaust fan, air intake shutters, and a thermostat� A 16″ shutter fan, two 18″ intake shutters and a thermostat costing about $460, has a 2000 CFM rating� It is best to install a variable speed fan that operates from a two-stage thermostat or a variable speed controller that initiates different speeds of the fan� The advantage to this type of fan is to enable minimum cooling during sunny days with ambient temperatures below optimum for the greenhouse crops� Due to the “greenhouse effect,” the greenhouse air temperature heats up fast under sunny conditions regardless of the outside temperature� The exhaust fan starts at a lower speed to exchange the air slowly, but keeping it within optimum levels� If the temperature in the greenhouse continues to rise above optimum, a faster fan speed will be initiated� This prevents a rapid influx of cold air into the greenhouse� The slowly incoming air will mix with the inside air keeping it optimum around the plant canopy�

Locate the exhaust fan on the north end of the greenhouse above the nutrient tank at about 7 ft from the ground� Installation instructions are given in Figure 21�3� Mount the fan frame on horizontal support bars bolted to the vertical framework of the greenhouse� The motor on the fan is on the inside of the greenhouse with the shutters outside� Caulk the perimeter of the shutter to the greenhouse glazing� The two intake shutters are situated on the opposite end, one on each side of the door, about 18″ above ground level� These intake shutters may operate with the pressure difference created during the exhaust fan activation as shown in Figure 19�23 or they may be regulated by a small motor that is coordinated with the operation of the exhaust fan�

Thermostat and speed control units should be mounted at plant height near the center of the greenhouse so as not to be influenced by drafts directly in line with the exhaust fan or heater� Protect them from direct sunlight by mounting them to a

piece of plywood painted white� Put a small top above them to shade them from the sun as shown in Figure 21�4�

Support one small circulation fan (10″ diameter) above each aisle between the crop rows� Locate one next to the door facing the opposite direction and the other at the exhaust fan end in front of the nutrient tank (Figure 21�5)� These fans will circulate and mix the air to make the temperature more uniform throughout the greenhouse� They cost less than $100�

As mentioned in Chapter 19, many backyard greenhouses have solar operated roof vents� This is a less expensive method of ventilation than forced air that depends

entirely upon convection air currents within the greenhouse� Under high summer sunlight and temperatures, natural ventilation may be inadequate� Under such conditions, cooling can be assisted greatly by the use of an evaporative cooler or the use of an evaporative cooling pad on the end of the greenhouse opposite the exhaust fan�

There are two methods of cooling: evaporative cooling and fogging systems� With an evaporative cooling pad two exhaust fans are part of the system� Locate the evaporative cooling pad on the north end above the nutrient tank and two exhaust fans on the opposite, entrance end of the greenhouse� If the greenhouse has natural solar vents, they must be closed (disabled) during a cooling cycle to prevent short-circuiting of the air entering directly from the roof vents and bypassing the cooling pads�

The size of the cooling pads is a function of the total CFM of air to be exchanged� In our 10 ft × 12 ft greenhouse, we needed 1440 CFM� For 4″ thick cooling pads use 1 sq ft of pad per 250 CFM� That would be: 1440/250 = 6 sq ft� The smallest self-contained cooling pad systems come 3 ft wide by 5 ft long and are capable of cooling about 4000 cubic ft� So, such a unit would be more than adequate for our 120 sq ft greenhouse�

However, smaller units can be made upon request from suppliers� The reservoir, collection pipe and inflow pipe of a self-contained unit are constructed of polyvinyl chloride (PVC)� This eliminates the need for a separate external sump tank as it along with all the piping (outflow distribution pipe over the top of the pad and the bottom return pipe) connect to a small PVC reservoir that has a submersible pump as shown in Figure 21�6� This could be constructed as a do-it-yourself (DIY) project by simply purchasing some 4″ thick cooling pads of 2-ft or 3-ft tall and make it 4-5 ft long� The cooling pad panels are 12″ wide by 2-8 ft tall in 1-ft increments� It would be best to use either 2 ft or 3 ft tall sizes� Locate the cooling pad in the middle of the north end of the greenhouse or that end above the nutrient tank� Place it to one side of the control panel 3-4 ft above the floor� A ready-made cooling pad system of 3 ft × 5 ft costs about $800�

It is best to choose two exhaust fans that have a larger capacity than the 1440 CFM as the static pressure though the cooling pad reduces the air flow slightly� Therefore, the total rate of air exchange of the two exhaust fans should be about 2500 CFM�

An alternative to using a cooling pad system is to use an evaporative cooler (Figure 21�7)� This is the preferable method for small greenhouses� They come in numerous sizes ranging from 1000 to 6500 CFM with prices ranging from $400 to $1300� Two types available include through wall and ducted models� The coolers are situated outside the greenhouse at the north or tank end wall� It is best to support the cooler on a concrete pad to keep it free of dirt and debris� Provide access through the greenhouse covering to fit the discharge of the cooler� This cooler is selfcontained with a blower that moves outside air across cooling pads inside the unit and pushes cold air into the greenhouse� As a positive pressure system, it forces the hot air in the greenhouse out roof vents or exhaust shutters as shown in Chapter 19 (Figures 19�25 and 19�26)� The system is operated by a two-stage thermostat that runs the cooler with or without wetting the pads� The first stage is a dry pad and as the temperature reaches a second limit, the pad is moistened to further reduce the temperature� The coolers come with a water hose connection for constant water supply� Be sure to match the CFM ratings of the cooler with the total of the exhaust shutters or roof vents� Be careful to winterize the evaporative cooler by draining all water from the system before any threat of frost�

A very simple method for additional cooling is to attach a mist ring on the outside protector cage of circulation fans within the greenhouse (Figures 21�8 and 21�9)� These mist rings emit a fine mist (1/2 gph per nozzle) that is dispersed throughout the greenhouse by the fan cooling the air while also adding humidity� Attach the mist ring to a standard water hose� They are available in three sizes depending upon the fan size, using 3, 4, and 5 nozzles per ring� The ring is easily attached to the fan cage by use of plastic zip ties� Connect a water filter on the garden hose or hose bibb in line with the mist ring to prevent clogging of the mist nozzles with debris� The mist rings range in price from $25 to $30 for the different sizes�

Fogging is an efficient cooling method, but unfortunately most systems are expensive and more applicable to large greenhouses� Such systems operate at a water pressure of 1000 psi in order to produce droplets of 5-45 microns� At that size, the water particles remain suspended in the air as a fog, not a mist� The evaporation into the air of the water lowers the air temperature� To generate such fine water droplets a high pressure pump, flexible tubes, filter, and nozzles make up the components of the system� Even the smallest portable units are for an air volume of 5000 cubic ft, about four times that needed for our 10 ft × 12 ft example backyard greenhouse� The fogging nozzles are attached to the cage of a very high velocity fan that would damage the crop in a small greenhouse� Other small portable humidifiers are those used in homes to increase the relative humidity in the air� These can be used in a backyard

greenhouse� They are operated by a humidistat located 5-6 ft above the floor� The humidistat is connected in series with the fogger� It will control the fogger within a 20%–80% humidity range� A typical humidifier of this type is the “Hydrofogger” at www�hydrofogger�com (Figure 21�10)� This unit is recommended for small greenhouses and indoor gardening with air volumes of up to 4500 cubic ft� They also have a smaller “Minifogger,” which covers up to approximately 1080 cubic ft and a “Cuoghi Mini NEB” that covers up to 1980 cubic ft� Prices range from $300 to over $600�

Partial shading, up to 40%, is recommended during the longest, hottest days from late spring to early fall� The shade cloth can be placed on top of the greenhouse roof� The shade will assist in reducing some of the heat entering the greenhouse and therefore save on the evaporative cooling� Avoid resting the shade cloth directly on the greenhouse covering, especially if the glazing is glass or polycarbonate� Place a few bars across the roof to keep the shade several inches above� This will permit some ventilation between the shade and the glazing and will avoid any possible adhering of the shade cloth to the glazing under high temperatures� If you do not want to cover the greenhouse with shade cloth, use whitewash paint over the hottest months� It can be washed off easily in mid-fall so as not to limit light as the days shorten� An excellent product is “ReduSol” by Mardenkro (www�mardenkro�com)�

Supplementary artificial lighting is essential to increase yields and shorten cropping cycles during the short day lengths and low light levels of late fall through winter to early spring months� Plant growing lights include cool white, high-output fluorescent, high intensity discharge (HID), light emitting diode (LED), and compact fluorescent lights as shown in Figures 21�11 through 21�14� The choice of light is a function of light demand of the specific crops, capital cost, operational cost, and the area served by a given unit�

There are two types of high intensity discharge (HID) lights: high-pressure sodium (HPS) and metal halide (MH)� The HPS lights provide more energy in the red part of the spectrum, which promotes flowering and fruiting, while the MH lights are more intense in the blue causing rapid growth� HPS lights are better to

supplement sunlight to extend the day length or to increase intensity during cloudy periods whereas MH light is more useful for indoors without natural sunlight� These lights give off considerable heat so must be mounted about 3 ft above the crop� With the relatively low eave height of backyard greenhouses, it is not possible to mount these lights above the crop� The alternative is to mount one unit near the peak of the roof in the middle of the greenhouse� This position of the light unit reduces the efficiency of the light distribution as the plants directly below will receive more light than the rows next to the sides of the greenhouse� Another disadvantage is that the lights are expensive to purchase and operate�

For small backyard greenhouses fluorescent lights are more efficient� The new T5 lights put out more intensity than older fluorescent lights� They have the advantage of offering higher light efficiency with low heat and provide a full spectrum in the red and blue for plant growth, flowering, and fruiting� They are available as a high output tube that provides about twice the intensity of light than the standard T5 tube� They are available as single tubes or multiple tubes, up to 8, in a 4-ft reflector unit (Figure 21�12)� A single unit fixture and bulb costs about $50� Although they do not have the intensity of HID lights, they can be placed within 6-18″ of the plant due to cooler output and therefore can give similar intensity at plant leaf surface� These

fluorescent lights are lighter in weight and have lower profile� Their ballasts may be remotely located to further reduce any heat generated directly above the plants�

LED lights are very light in weight, generate very little heat, and have very long life� They maximize red and blue light so are well balanced for the vegetative and flowering growth of plants� However, to get sufficient intensity and uniform distribution of the light it is necessary to purchase LED arrays where many LED lights of white, red, and blue combinations fit within a reflector unit (Figure 21�13) that will produce an equivalent of a 1000 watt HID lamp� Prices of these arrays are high from $1000 to $1200 each�

How much lighting is needed? Most vegetable crops need 50-70 watts of light per square foot of growing area if the artificial light is the only source of light� In a backyard greenhouse that has natural light also available, the level of supplementary lighting can be reduced to one-quarter of that� Calculate the correct wattage of light needed for a specific area by multiplying the desired wattage of the light by the area in square feet� In our greenhouse example of 10 ft × 12 ft the total area is 120 sq ft� So, we need at least 50 watts × 120 sq ft × 25% = 1500 watts� One 1000-watt HID light mounted near the peak of the greenhouse would provide this amount of light as would an LED light array� My preference for a backyard greenhouse is to use three 8-ft, dual tube, high-output fluorescent units, one above each row of plants� With the 4-ft T5 high output four tube fixtures use a total of 6 units� The cost for those would be about $800�

Support the fluorescent lights about 18″ above the tops of the plants using jack chains that will allow their adjustment as the crop grows�

Compact fluorescent lights with fixtures (Figure 21�14) (one bulb per fixture of 125 watt) will cover a maximum of 3 ft × 3 ft of growing area� For our greenhouse example we would need 4 units per row or a total of 12 units� These cost about $70 a unit, so while the lights last about 10,000 h the number of units needed is not practical compared to other light sources as the cost for 12 units is over $800�

With a single unit of HID or LED array, it is advantageous to use a light mover that moves the light back and forth on a track above the crop to give better light distribution over time (Figures 16�5 and 16�6)� This gives better light penetration throughout the crop than just those plants immediately below the light unit� Supplementary light is also for extending the day length during the winter months�

Keep day length at 12-14 hours, as plants need a period of darkness� In addition, you do not want to upset any neighbors by lighting the greenhouse beyond normal summer months of daylight� Operate the lights with a time-clock, starting them about 8:00 AM and turning them off by 10:00 PM� That will give 14 h of supplementary light� On days with sunlight, turn off the lights by 9:00 AM and activate them again about 3:30 PM in the afternoon as the sun intensity falls� It is also possible to get a photo sensor that could regulate the operation of the lights�

While the exhaust fan, roof vents, and heaters can be controlled with thermostats, the irrigation cycles are operated by a time-clock or controller� Irrigation controllers offer more functions than a simple time-clock, but are relatively expensive� Time-clocks

should be of 24-h periods with intervals capable of separate hours and minutes� There are electronic 7-day programmable timers having 1 min on/off cycles with up to eight cycles per day for about $25 (Figure 21�15)� This programmable timer is ideal for activating irrigation cycles� For about $15 you can purchase a mechanical timer that has 15 min on/off cycles with a 24-h time period (Figure 21�16)� This type of timer is fine for turning lights off and on, but is not suitable for irrigation cycles� A time-clock will operate as only one station, so it does not have the capability to operate different irrigation cycles and periods for different rows of crops� To achieve this use an irrigation controller having at least three to four stations� To operate independently several stations solenoid valves are installed within each irrigation line to the plants� These would be located near the header pipe after the ball or gate valve,

but before the conversion to the black poly hose having the drip lines� These solenoid valves would be for ¾″ diameter pipe as that is the pipe size from the header�

Many irrigation equipment suppliers, such as Hunter Industries, Rain Bird, and Toro have controllers for home landscapes (See Appendix)� The least expensive controllers (under $300), which have four stations, have only four starts per station during a day� That is not enough for irrigating during hot days when you may need at least 8-10 starts�

There are also timer switches (time-clocks) at lower prices from $25 to over $250 that turn one output on or off over a period of 7 days and can be adjusted to within 1 min intervals� The electronic versions are the expensive ones� Electromechanically operated timers are at the low price range� Intermatic (www�intermatic�com), Tork, and Paragon make both mechanical and electronic timers that vary in price from $100 to over $350� They are available through Grainger, Inc� (www�grainger�com) as are many other components as fans, heaters, vents, and so on� The lowest price timeclocks are 7-day clocks that can activate a circuit for a minimum of 15 min�

Using a 2-pole relay, these timers can activate one 110-120 volt circuit (pump) and a 24-volt circuit (solenoid) at the same time using a step down transformer in parallel with the solenoid, but they act as only one station� This restricts their ability to operate the pump and two solenoids at different times as that would require a twostation controller or two independent time-clocks� Each electronic time-clock costs about $175� The low-priced timers are used to turn lights on and off, such as those used in households that are available for $25 or less�

After examining many of these controllers and timers, I believe that a low-priced timer is fine for operating the lights but cannot be used for irrigation� Overall, the best procedure is to operate all of the plant rows at the same time on one time-clock that activates the pump only� When growing all vine crops with drip irrigation on a small scale, there is no significant benefit of increased yields by using different irrigation cycles for different plant rows� Grow low-profile plants such as herbs, lettuce, and basil in a separate nutrient film technique (NFT) or raft culture system that is operated independently of the vine crops� If you wish to grow these crops in plant towers with a drip irrigation system, keep them on the same cycles as the vine crops operated by the same pump� The 7-day programmable timer for about $25 is suitable for these needs�

While some of these components seem to be complicated in their specifications for your specific needs, salespersons in companies distributing the products can assist greatly in simplifying your choices to suit your greenhouse needs� These are all on-the-shelf products available at many distributors in stores or online�