Carbon dioxide (CO,) is a colorless, odorless, non-flammable gas that is around us all the time. The air we breathe contains 0.03-0.04 percent CO,. Rapidly growing cannabis can use all of the available CO, in an enclosed grow room within a few hours, Photosynthesis and growth slow to a crawl when the CO, level falls below 0.02 percent.
Carbon dioxide enrichment has been used in commercial greenhouses for more than 35 years. Adding more CO, 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 , than the 0.03-0.01 percent (300-400 ppm) that naturally occurs in the air. By increasing the amount of CO, 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,.
*Carbon dioxide can make people woozy when it rises above 5000 ppm and can become toxic at super high levels. When CO, 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, 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 refeased into the air by the same stomata the plant uses to absorb CO, during transpiration. Carbon dioxide enrichment affects transpiration by causing the plants' stomata to partially close. This slows down the loss of water vapor into the air. Foliage on CO,-enriched plants is measurably thicker, more turgid, and slower to wilt than leaves on non-enriched plants.
Carbon dioxide aflects 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 CO, enrichment is used.
With CO,-enriched air, plants that do not have the support of the other critical elements for life will not benefit at all, and the CO, 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, the CO, 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 CO, from escaping. Enclosing the room makes it easier to control the CO, content of 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 CO,-enriched
air. The flaps or baffle will help contain the CO, in the enclosed grow room. Venting requirements will change with each type of CO .-enrichment system and are discussed below.
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