Chapter Eleven - Four Ways to a Better Grow Room

I know a person with a very observant eye and a keen sense of the possible. One day we were walking through a commercial area where men were unloading boxes from a truck. ‘Fred’ asked to see the manager, and told him that he could improve the effi- ciency of the operation by 30 percent if he was paid $100. The manager agreed to pay if it worked. Fred showed the manager that the men were loading only two boxes on each truck, while, if the boxes were loaded sideways, the trucks could hold four. The man- ager reluctantly wrote a check.
On the way out, Fred said, “I can still cut unloading time by 30 percent for $50.” The manager shook his head, but as we began to leave he called us back and agreed. Fred told him to increase the length of the platform on the hand trucks by attaching a board to them. The manager handed Fred a President Grant, shaking his head with an ‘I should have known’ look. A study of any operation will reveal many areas for improve- ment. Even seasoned experts can overlook fundamental principles. For example, take two gardens, “A” and “B”, maintained by experienced cultivators:

Garden A is lit by two vertical 1000-watt metal halide (MH) lamps with wide reflectors on a rotating light mover. There is an aisle between the wall and the garden. The plants grow in 3-inch cups filled with expanded clay, placed in 9-inch tubes. They are irrigated by two constant-flow sprayers aimed at each cup.

Both gardens will lose yield because the growers neglected to apply some basic principles when setting up the grow rooms. Here are four ways to bring these gardens to full potential:

Maximize light distribution to the plants. Plants use light to power photosynthesis, the process by which carbon dioxide and water are turned into sugar and oxygen. The more light the plants receive, the more sugar is produced, and the faster they grow. Both Gardens A and B waste light. In garden A, as the horizontal lamps travel around, much of the light is used to illuminate the aisles around the perimeter. In garden B, the bottom of the vertical lamp hangs below the reflector and much of the light travels horizontal- ly across the room, hitting the walls.
- In both grow rooms, the walls are covered with black plastic, which absorbs light and emits heat. Placing a reflec- tive curtain around the garden perimeter could increase the amount of light received by the plants by as much as 20 percent. Curtains can be hung from the ceiling or from rods. Moveable reflective panels can also be used. Panels can be made from 4’ x 8’ Styrofoam pieces coated in a reflective material. Most growers prefer Mylar, but aluminum foil, silvered gift wrap, aluminized greenhouse white paint and flat white paint all work.

Provide adequate support to each of the plants. When shaded, plants lose the energy they need for fast growth. If plants are properly supported, they won’t shade each other. This ensures that each plant has the necessary light and space to grow to its full potential.
- The plants in Garden A are supported with an appropri- ate bamboo stake, but the plants in Garden B have no support. Neighboring plants are crowding over onto one another, shading the canopies and lowering growth rate and yield. The problem can be solved in several ways. Each plant can be supported by a bamboo stake secured with twist ties to keep the central stem erect. Alternatively, a small cage, such as a tomato cage, can be placed around each cup. A third option is to run a small fence along the length of each tube, attaching the plant stem with twist-ties. Rows of strings can be hung from the ceiling or overhead rods and connected to the plants.
Focus light where it is needed most. Stretching can occur when plants crowd each other for canopy space. Lower parts of the plant tend to stretch as a higher ratio of infrared light, rather than direct red light, reaches the lower canopy. Light can be reflected back from the floor to target the lower plant sections. This unfil- tered light is higher in red, counteracting the stretching effects of the infrared light.
- The floors of both gardens are covered with dull-colored plastic tarps, and because of the plant spacing, much of the light hits the floor. Covering the floor with white plastic, Mylar or bright white posterboard, increases the amount of light received by the plants, and prevents stretch- ing by targeting the lower canopy.
Use CO₂ to increase yield. The addition of a CO₂ source can dramatically increase yield. Photosynthesis uses light to power a complex reaction in which hydrogen (H), carbon (C) and oxygen (0), from water (H₂0), and carbon dioxide (C0₂) combine to form sugar (C₆H₁₂0₆). The ambient level of CO₂ in air is about 400 parts per million. In a closed environment under bright light, the plants quickly lower the CO₂ levels as the 0 levels increase. When levels of CO₂ go down to 200 ppm, photosynthesis stops.
- Plant growth increases in a direct ratio to CO₂ levels until another limiting factor (usually light) is encountered. Indoors, with bright lights, plants can use 1000 to 1500 ppm CO₂. This is most easily supplied using a CO₂ tank and regulator. Some of these regulators are time based, others work in conjunction with the ventilation; the most sophisticated measure the amount of CO₂ in the air. Plants grow much faster, and produce heavier yields, when they receive CO₂-enriched air right up until the last two weeks of flowering.