Marijuana Horticulture: The Indoor/Outdoor Medical Grower's Bible
water or setting out a bucket of water to evaporate into the air. A humidifier is convenient and relatively inexpensive. Humidifiers evaporate water into the air to increase humidity. Just set the dial to a specific humidity, and presto! The humidity changes to the desired level as soon as the humidifier is able to evaporate enough water into the air. A humidifier is not necessary unless there is an extreme problem with the grow room drying out. Problems seldom occur that can be remedied by a humidifier. All too often, there is too much humidity in the air as a result of irrigation and transpiration. If a ventilation system is unable to remove enough air to lower humidity, a dehumidifier could be just the ticket!
A dehumidifier removes moisture in a room by condensing it from the air. Once the water is separated from the air, it is captured in a removable container. This container should be emptied daily. It is easy to remove and catch 10 ounces (0.3 L) of water in a 10 × 10 × 8-foot (21.5 m 2 ) room when the temperature drops just 10°F (5°C).
A dehumidifier can be used anytime to help guard against fungus. Just set the dial at the desired percent humidity and presto, perfect humidity. Dehumidifiers are more complex, use more electricity than humidifiers, and cost more, but to growers with extreme humidity problemsnot yet cured by a vent fan, they are worth the added expense. The best prices on dehumidifiers have been found at Home Depot, Home Base, and other discount stores. Check the rental companies in the Yellow Pages for large dehumidifiers if only needed for a short time. Air conditioners also function as dehumidifiers but use a lot of electricity. The water collected from a dehumidifier or air conditioner has a very low EC and can be used to water plants.
Note: Air conditioners draw moisture from the air and lower the humidity. The moisture condenses into water that is collected in a container or expelled through a tube outdoors. The condensed water carries the fragrance of cannabis. Sniffer dogs can easily smell the fragrance of cannabis in the “tainted” water expelled outdoors.
Rooting clones thrive when the humidity is from 70 to 100 percent. Under arid conditions, the undeveloped root system is not able to supply water fast enough to keep clones alive. See “Clones and Cloning” for more specific information on humidity levels during different stages of cloning.
CO 2 Enrichment
Carbon dioxide (CO 2 ) is a colorless, odorless, nonflammable gas that is around us all the time. The air we breathe contains 0.03-0.04 percent CO 2 . Rapidly growing cannabis can use all of the available CO 2 in an enclosed grow room within a few hours. Photosynthesis and growth slow to a crawl when the CO 2 level falls below 0.02 percent.
Carbon dioxide enrichment has been used in commercial greenhouses for more than 35 years. Adding more CO 2 to grow room air stimulates growth. Indoor cannabis cultivation is similar to conditions in a greenhouse, and indoor growers apply the same principles. Cannabis can use more CO 2 than the 0.03-0.04 percent (300-400 ppm) that naturally occurs in the air. By increasing the amount of CO 2 to 0.12-0.15 percent (1200-1500 ppm)–the optimum amount widely agreed upon by professional growers–plants can grow up to 30 percent faster, providing that light, water, and nutrients are not limiting. Carbon dioxide enrichment has little or no affect on plants grown under fluorescent lights. Fluorescent tubes do not supply enough light for the plant to process the extra available CO 2 .
*Carbon dioxide can make people woozy when it rises above 5000 ppm and can become toxic at super high levels. When CO 2 rises to such high levels, there is always a lack of oxygen!
Carbon dioxide enrichment does not make plants produce more potent THC; it causes more foliage to grow in less time. The larger the volume of THC-potent cannabis, the larger the volume of THC produced.
Carbon dioxide-enriched cannabis demands a higher level of maintenance than normal plants. Carbon dioxide-enriched plants use nutrients, water, and space faster than non-enriched plants. A higher temperature, from 75 to 80°F (24 to 26°C) will help stimulate more rapid metabolism within the super-enriched plants. When temperatures climb beyond 85°F (29°C), CO 2 enrichment becomes ineffective, and at 90°F (32°C) growth stops.
Carbon dioxide-enriched plants use more water. Water rises from plant roots and is released into the
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