CO2 Enrichment
Marijuana Horticulture
by Jorge Cervantes
Carbon dioxide (CO2) is a colorless, odorless, nonflammable gas that is around us all the time. The air we breathe contains 0.03-0.04 percent CO2. Rapidly growing cannabis can use all the available CO2 in an enclosed grow room within a few hours. Photosynthesis and growth slow to crawl when the CO2 level falls below 0.02 percent.
Carbon dioxide enrichment has been used in commercial greenhouses for more than 35 years. Adding more CO2 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 CO2 than the 0.03-0.04 percent that naturally occurs in the air. By increasing the amount of CO2 to 0.12-0.15 percent – 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 effect on plants grown under fluorescent lights. Fluorescent tubes do not supply enough light for the plant to process the extra available CO2.
Carbon dioxide can make people woozy when it rises above 5000 ppm and can become toxic at super high levels. When CO2 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 high temperature, from 75 to 80F will help stimulate more rapid metabolism within the super enriched plants. When temperatures climb beyond 85F, Co2 enrichment becomes ineffective, and at 90F growth stops.
Carbon-dioxide enriched plants use more water. Water rises from plant roots and is released into the air by the same stomata the plant uses t absorb CO2 during transpiration. Carbon dioxide enrichment affects transpiration by causing the plants’ stomata to partially close. This slows down the loss of water vapor int the air. Foliage on CO2 enriched plants is measurably thicker, more turgid, and slower to wilt than eaves on non-enriched plants.
Carbon dioxide affects plant morphology. In an enriched growing environment, stems and branches grow faster, and the cells of these plant parts are more densely packed. Flower stems carry more weight without bending. Because of the increased rate of branching, cannabis has more flower initiation sites. Plants that sometimes do not bear from the first flower set are more likely to set flowers early if CO2 enrichment is used.
With CO2 enriched air, plants that do not have the support of the other critical elements for life will not benefit at all, and the CO2 is wasted. The plant can be limited by just one of the critical factors. For example, the plants use water and nutrients a lot faster, and if they are not supplied, the plants will not grow. They might even be stunted.
To be most effective, CO2 level must be maintained at 1000 to 1500 ppm everywhere in the room. To accomplish this, the grow room must be completely enclosed. Cracks in and around the walls should be sealed off to prevent CO2 from escaping. Enclosing the room makes it easier to control the CO2 content f the air within. The room must also have a vent fan with flaps or a baffle. The vent fan will remove the stale air that will be replaced with Co2 enriched air. The flaps or baffle will help contain the CO2 in the enclosed grow room. Venting requirements will change with each type of Co2 enrichment system and are discussed below.