Marijuana Horticulture: The Indoor/Outdoor Medical Grower's Bible

feathers on a duck and shed water.
     
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    Stomata close when there is:
    Too much CO 2
    Low humidity
    A dry root system
    Stomata open when there is:
    High light
    Low CO 2
    High Humidity
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    Earth Juice Wetting Agent
Foliar Feeding
    Foliar feeding means to spray the nutrients or bio-stimulants onto the foliage to augment available nutrients, vitamins, hormones, etc. Timing is key to achieving the best coverage and absorption. The waxy (cuticle) surface coating (cystolith hairs and resin) on cannabis foliage makes them very poor water absorbers. This barrier wards off pest and disease attacks, but it also slows the penetration of sprays.
    Young leaves are more permeable than older leaves. Nutrients and additives penetrate immature leaves faster than tougher, older leaves, and they are easier to damage with strong sprays.
    Foliar feed the cannabis plants only when specific deficiency symptoms manifest. Foliar feeding is a quick fix only and is easy to overdo. High levels of nutrients in the foliage stop the roots from taking in more; this is confusing for the plant. Foliar sprays can accumulate and build up in the foliage. Never spray more than once every 10 days, and keep the spray concentration to less than 500 ppm or with an EC of less than 1.0.
Spreader-Stickers
    Smart growers use a surfactant, surface-active substance (adjuvant), which enhances the effectiveness of foliar fertilization.
    Spreaders (wetting agents) reduce the surface tension of sprays and keep them from beading up and rolling off the foliage. Big, bulbous drops on the leaves mean you need to use a spreader. Flat drops that slide off the foliage mean there is too much spreader. There are nonionic, antionic, and cationic spreaders. The nonionic spreaders that do not ionize in water are the most common, and they do not react with most pesticides. Antionic and cationic spreaders are not used often.
    Stickers help the spray adhere to the leaf after spraying, so it does not wash off when it rains or when dew forms. Stickers not only increase adhesion, they slow evaporation, and impart a waterproof coating. Some stickers are spreaders, too. Spreader-stickers allow the stomata on the leaves to be penetrated.
    Extender (stabilizing agents) protects applied sprays against the UV radiation and heat that degrade the sprays.
    Liquid and powder soaps and detergents act as surfactants, too. But, they are not nearly as effective as horticultural surfactants. Biodegradable surfactants disappear the fastest. Silicone surfactants are also mild insecticides that work to impair pest functions.
    Foliar spray concentration is cumulative. Nutrients delivered via the foliage can cause a buildup of salts in and around the leaves. This is similar to the way the salts accumulate in the soil.
    Overfertilizing can become one of the biggest problems for indoor growers. Too much fertilizer causes a buildup of the nutrients (salts) to toxic levels, and it changes the soil chemistry. When overfertilized, growth is rapid and lush until the toxic levels are reached. At this point, things become complicated.
    Chance of overfertilization is greater in a small amount of soil that can hold only a small amount of nutrients. A large pot or planter can safely hold much more soil and nutrients, but it will take longer to flush if overdone. It is very easy to add too much fertilizer to a small container. Large containers have good nutrient-holding ability.
    To treat severely overfertilized plants, leach the soil with two gallons (8 L) of diluted nutrient solution per gallon (4 L) of soil to wash out all excess nutrients. The plant should start new growth and look better in one week. If the problem is severe and the leaves are curled, the soil may need to be leached several times. After the plant appears to have leveled off to normal growth, apply the diluted fertilizer solution.
Additives
    Numerous additives or growth supplements have hit the market over the last few years. Generally, additives contain a cocktail of some of the elements listed below. Most of the additives came from the greenhouse industry or were developed for organic growers. Many of these additives do what they say they will do and work quickly; however, when growing a short eight- to ten-week crop, some of these additives do not have time to work properly if added near the end of the flowering cycle.
    The following list will give you an idea of what specific additives are and how they are used.
Abscisic acid