Dry ice gets very expensive with prolonged use. Two pounds of dry ice will raise the CO, level in a 10 x 10-foot (3 nv) grow room to about 2000 ppm for a 24-hour period. One chagrined grower remarked, "I can't believe that stuff melts so fast."

Growers have long used large, insulated tanks filled with dry ice to add CO,. Dry ice is carbon dioxide that has been chilled and compressed. As it melts, it changes from solid to gas. Gaseous CO, can be mixed into the air with fans that circulate it among the plants. Dry ice works well on a smaller scale without a tank and converter. It is readily available (check out the Yellow Pages) and inexpensive. Because CO, has no liquid stage, the transformation from solid to gas as the ice melts is clean and tidy. It's also easy to approximate the amount of CO, being released. A pound of dry ice is equal to a pound of liquid CO.. Determining the thawing period for a particular size of dry ice will allow you to estimate how much CO, is released during a particular time period. To prolong the thawing process, put dry ice in insulating containers such as foam ice coolers, and cut holes in the top and sides to release the CO,. The size and number of holes allow you to control the rate at which the block melts and releases CO,.

Dry ice is economical and risk free; it releases no toxic gases, heat, or water. Although dry ice is easier to handle than compressed CO, tanks, it is difficult to store. The melting can be slowed through insulation, but it cannot be stopped. Because it is extremely cold, dry ice can also cause tissue damage or bum the skin after prolonged contact.

Growing Soilless

Growing Soilless

This is an easy-to-follow, step-by-step guide to growing organic, healthy vegetable, herbs and house plants without soil. Clearly illustrated with black and white line drawings, the book covers every aspect of home hydroponic gardening.

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