ABSTRACT
Environmental conditions must be maintained at optimum levels to achieve success with any indoor growing� These factors have to be monitored and regulated with equipment having sufficient capacity for the growing area (Figure 16�1)� The following factors are controlled: temperature, air circulation, carbon dioxide (CO2), light, water quality and temperature, nutrient solution pH and electrical conductivity (EC), and oxygenation of the nutrient solution when using water culture systems� The following discussion looks at each environmental factor to control and equipment that can fulfill that need�
Most plants grow well under specific temperature ranges� They require minimum and maximum levels� In general, night temperatures should be cooler than day temperatures� This differential may be as high as 10°F (5�5°C) or more� For cool-season crops such as lettuce, night temperatures should be about 55°F (13°C) and from 60° to 65°F (15�5-18°C) during the day� With warm-season crops such as tomatoes, peppers, cucumbers, and eggplants, suitable temperatures are 65°F (18°C) at night and 75°F (24°C) during the day� Herbs withstand a wider range of temperatures�
To control temperatures, a heating and cooling system is required� In most cases, in your home the normal temperatures you maintain in the house are within the desired temperature ranges of plants� If growing in a cool basement, a supplementary heating system may be a requisite� Electrical space heaters will meet the plant temperature demands� Use a 220-volt heater to save on the electrical demand� Baseboard heaters would also be good� These could be installed together with your house heating system� Artificial lights for providing light will also generate heat, so they may provide more than what is necessary to maintain optimum temperatures� In such a case, a cooling system will have to be installed to extract the air from the growing room�
Cooling by exhaust fan(s) is the standard method� The exhaust fans are installed in the wall with an outlet to the outside� Any such fan needs automatic shutters that close when not operating to assist in preventing insects from entering the growing room� The size of the fans is calculated on the volume of air in the growing room and the temperature differential that must be reduced within the room� An air exchange of the total volume should be at least one per minute if a significant number of lights
are installed� It is useful to have two-speed fans so that if a small amount of cooling is needed, the lower fan speed operates, but if further cooling is demanded the second faster speed is activated by a thermostat�
It is a good idea to purchase a thermograph that will record temperatures on a 24-hour basis� Some have charts that are good for a week of monitoring before replacing� The thermograph is much better than a max-min thermometer as the thermometer tells you only the maximum and minimum temperatures reached at an undesignated time� It does not tell you temperature fluctuations over time as does the thermograph�
Air temperature must be uniform throughout the crop canopy for optimum growth� As the plants grow vertically in the room, they block the circulation of air and cause large temperature differences from the bottom to the top of the plants� This, of course, is especially noticeable with vine crops� The ideal source of heat for the plants is to have floor or bottom heating pipes� Alternatively, a unit heater connected to convection tubes that are located between the rows of vine crops will make hot air rise up through the crop� However, with space heaters a convection tube cannot be used due to the fire hazard� If you mount a gas fired unit heater at one end of the room near the ceiling and install a housing that will distribute the heated air down through convection tubes to the base of the plants, you will get more efficient use of the heat than a space heater� This will also help
mix the air and create good circulation making the air temperature throughout the crop more uniform�
The mixing of the air is also important in exchanging the air at the boundary layer immediately in contact with the plant leaves� This movement of air past the leaves brings in fresh air high in CO2 in contact with the stomates of the leaves where the CO2 can enter the plant� Another helpful piece of equipment is a horizontal air flow fan (HAF) that is mounted near the ceiling� The HAF fan blows the air down the length of the room causing turbulent flow that mixes the air� This improved air circulation gives more uniform temperature and increases CO2 exchange at the leaves� Refer to the Appendix for suppliers of this equipment�
Normal CO2 levels in the ambient atmosphere are now approaching 400 mg/L or ppm� Research over the years has established that enrichment of CO2 to 2-3 times ambient levels (800-1200 ppm) greatly increase the production of vegetable crops by as much as 20%, especially under low light conditions� The ambient CO2 levels vary with your location� Cities have higher levels of CO2 due to automobiles and industries� There are a number of small CO2 generators available for home growers (Figure 16�2)� You can use bottled CO2 in tanks similar to propane tanks, but such a system is awkward and heavy to move for refilling� Also, when using tanks, a system of distribution tubes must be located between and underneath the rows of plants� Another system is a natural gas combustion unit that generates CO2� This CO2 generator also gives off heat that may have to be extracted as it operates only during the day period� The operation of the unit is governed by a timer�
The level of CO2 in the grow room must be monitored and regulated� Many of the generators have a monitor-controller that activates the enrichment system according to preset levels and turns it off if this level is exceeded� You may also purchase a hand-held tester for CO2 levels�
One of the least expensive and natural methods of generating CO2 is with a special CO2 composting pot that releases CO2 from the decomposition of mushroom compost (Figure 16�3)� One bucket will enrich a 10 ft × 10 ft × 10 ft room at levels between 1200 and 1500 ppm for 60-90 days� This is available commercially as a small bucket and is renewable with the purchase of refills (see Appendix for supplier)�
Most plants indoors will grow relatively well under a light intensity of 5500 lux (510-foot candles) for a period of 14-16 hours per day� The function of light in photosynthesis and its measurement related to photosynthesis was explained in Chapter 5� In the past, cool-white fluorescent lighting was the type of light used for plant supplementary lighting� Now there are more energy-efficient and better quality lights sold such as the high-intensity discharge (HID) and compact fluorescent� There are two types of HID lights: high-pressure sodium (HPS) and metal halide (MH)� A combination of both gives best results� The HPS lights promote blooming and fruiting, whereas, the MH light causes more rapid vegetative growth� Compact fluorescents save electricity� They are now available for growing plants (Figure 16�4)� Again, a mixture of the red for flowering and blue for vegetative growing is best�
Today, light emitting diode (LED) lights are gaining popularity due to their energy efficiency� There are a number of types available for growing plants that mix red and blue lights in reflectors to maximize their efficiency in photosynthesis� While these lights last up to 50,000 hours, they are expensive�
All lights are placed in reflective fixtures to maximize the reflection and distribution of the light� There are three shapes of reflectors: parabolic, horizontal, and conical� Parabolic reflectors focus light on the plants by directing the light below
the horizontal plane and thus reducing glare to your eyes� Conical reflectors give more side light� Square-shaped reflectors are effective for square growing areas� Horizontal reflectors are recommended for HPS systems�
Ballasts for HPS lights should be located away from your plants to reduce heat build-up within the crop� Ballasts are not needed for compact fluorescent and LED lights� Keep ballasts off the floor as water could splash onto them� Lights must be mounted above the crop by hooks or jack chains from the ceiling� If you use jack chains, you can raise the lights as the plants grow keeping the lights at least 2-3 ft above the crop� If the lights are too close, the heat they give off will promote rapid vegetative growth�
There are also circular and linear light movers that move the lights above the crop over a period of time to more evenly distribute the light intensity over the crop (Figure 16�5)� Linear movers are best for narrow growing areas, whereas circular movers are better for square areas� Light movers do not allow you to plant your crop at higher densities; they improve the light distribution and therefore produce a more even growth of all the plants (Figure 16�6)�
Use a Mylar reflective covering on the walls surrounding the hydroponic systems to reflect light back into the sides of the plants�
Refer to the Appendix for suppliers of lights and their accessories�
Water quality and temperature are important factors for successfully growing plants� Water quality is a measure of the types and concentrations of minerals present in the raw water� Most city waters are of acceptable quality, unless they are very “hard�” Hardness is a measure of the amount of calcium and magnesium carbonate present in the water� Hard waters are quite suitable for hydroponics� The only thing you must determine is which elements and at what concentrations they are present so that you may adjust your nutrient solution formulation accordingly� If you purchase a ready-made formulation, ask for one that is for hard water� If you make up your own formulation, hard water may provide most of your calcium and magnesium needs, so will actually save on the use of the fertilizer salts required�
The best approach is to get a water analysis of the raw water by a laboratory that does such tests� Test for all of the plant essential elements� Once you know the levels, you can adjust the nutrient formulation to take those into account� When the analysis of the trace elements indicates some are high, reduce or even exclude those from the formulation� For example, optimum boron concentration for the plants is about 0�3 mg/L, so if the test shows boron in excess of that leave out any addition of it in the formulation� Most plants will tolerate boron levels twice or three times the optimum level before any reduction in growth occurs� Often information on water quality may be obtained from the city offices that regulate domestic water supply�
The temperature of the raw water is also a factor that affects plant growth� Everyone is aware that you do not start your soil garden too early in the spring when the soil and groundwater are very cold as the plants will not grow and often just survive without any new growth until the weather heats up the soil� With hydroponics, water temperature is also important for rapid growth� If the water is too cold, purchase an immersion heater� This type of heater is generally electric for small nutrient tanks� They should be available at local hydroponic shops (see Appendix)� The immersion heater is placed in the nutrient tank� Temperature is controlled with a thermostat on the immersion heater�
Keep the nutrient solution between 65 and 70°F (18-21°C)� Water may also be too high in temperature� In that case, use a water chiller to lower the nutrient solution temperature� For example, lettuce likes a cooler water temperature of 65-68°F (18-20°C)� If raw water enters at 80°F (27°C) or more, it is best to lower the temperature to prevent bolting (lettuce going to seed grows a shoot rapidly) and fungal activity in the roots that will damage the plants causing them to wilt during highlight conditions of mid-day� Water holds more oxygen at lower temperature so this also affects plant roots and growth� Alternatively, an ozone generator may be used to add oxygen to water, which will prevent diseases and slow any bolting of lettuce�
Controlling nutrient solution temperature is critical in growing crops in nutrient film technique (NFT) and raft culture systems, especially cool-season crops such as lettuce and spinach� Sources for these components are listed in the Appendix�
To monitor the concentration of nutrients in the nutrient solution use an EC meter (Figure 16�7)� Hand-held “pen” type EC meters are also available (Figure 16�8)� These meters tell the total dissolved solutes in the solution and therefore indicate when the
solution is being depleted of its elements� The addition of elements can be calculated and a “top-up” solution used to increase the elements� However, on a small scale it is much easier to simply replace the nutrient solution making up a new solution every few weeks� Plants use more water than nutrients, so the addition of water is needed every few days (depending upon the ratio of volume of water to each plant)� With a
larger solution tank, the make-up of water and nutrients is less frequent� The addition of water to a nutrient reservoir can be automated using a float valve�
The next factor to monitor is the pH of the solution� Test it every day and add an acid or base to lower or raise it, respectively� You may test it with an indicator paper similar to that used for fish aquariums (Figure 16�9) or a small hand-held pH meter (Figure 16�10)� These products are available at hydroponic stores (see Appendix)� You can also purchase “pH Up” and “pH Down” solutions from hydroponic outlets or online (Figure 16�11) as mentioned in Chapter 9�
This applies mainly to water culture systems� It is, however, helpful for all hydroponic systems to oxygenate the nutrient solution in the solution tank� Achieve this with an air pump and some air stones� These can be acquired from an aquarium shop or online (see Appendix)� Place the air stone(s) in the nutrient reservoir connected by poly tubing to the air pump� Keep the air pump elevated above the level of the tank to prevent any possible damage to the pump by water returning to the pump, should the power fail� For raft culture, place a series of air stones along the bottom of the raceway� Connect with poly tubing the air diffusers to an air pump� Many sizes and types of air pumps from linear piston air pumps to diaphragm pumps are available from fish culture suppliers such as Aquatic Eco-Systems, Inc� (www�AquaticEco�com)� They also sell tubing, fittings, and diffuser air stones�
Controlling all of these environmental factors at optimum levels will assist in the success of growing hydroponically� Hydroponic culture enables the grower to maximize production and quality� If one or more environmental factors are not at optimum level for the crop, the ability for hydroponics to maximize quality and yield will be restricted�
