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

minimum of nitrogen and increased levels of phosphorus to promote root growth. Sprays should be avoided during rooting as they compound cloning stress. Given good instruction and a little experience, most growers achieve a consistent, 100 percent clone survival rate.
    Large cuttings with large stems packed with starch grow roots slower than small clones with small stems. The excess starch in moist substrate also attracts diseases. Thin-stemmed clones have fewer reserves (accumulated starch), but they only need enough reserve energy to initiate root growth.
    Small clones with few leaves root faster than big cuttings with many leaves. At first leaves contain moisture, but after a few days, the stem is no longer able to supply enough moisture to the leaves, and the clone suffers stress. A small amount of leaf space is all that is necessary for photosynthesis to supply enough energy for root growth.

These ‘Ortega’ clones were taken on August 25. Now they are rooted and ready to transplant.
     
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    This chart shows average times for roots to grow from the cambium. Note: Clones taken from younger growth root about twice as fast as those taken from older growth.
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Precautions
    An embolism is a bubble of air that gets trapped in the hole in the stem. Embolisms occur when you take big clones and lay them on the counter before placing in water or a growing medium. When an embolism happens, fluid flow stops, and clones die. After taking cuttings, immediately dip them in water or a growing medium to prevent air from getting trapped in the hollow stems. Eliminate the threat of an embolism by taking cuttings under water.
    Clones root well within a pH range of five to six. Aeroponic clone gardens normally do best with a pH of five to five and a half. Most diseases grow poorly below these pH levels. Always make sure there is plenty of air in the rooting medium; this will stimulate root growth.
    Do not kill clones with kindness and fertilizer. At best, giving clones an excess dose of fertilizer causes rooting to be delayed. In fact, a good dose of ammonium nitrate, a common fertilizer, will stop root hairs from growing.
    If an infestation occurs, apply aerosol pyre-thrum. Remember, all pesticides, natural or not, are phytotoxic. Spraying cuttings is a bad idea in general. If you must use sprays, use natural organic sprays, apply them when it is cool, and keep their use to a minimum.
    Use anti-desiccant sprays sparingly, if at all, and only if a humidity dome is unavailable. Anti-desiccant sprays clog stomata and can impair root growth in clones.
    Do not over-water clones. Keep the medium evenly moist, and do not let it get soggy.
    Any kind of stress disrupts hormones and slows rapid growth.
    Keep the cloning area clean. Do not take clones where fungus spores and diseases are hiding! Pythium is the worst! Pythium flourishes in high temperatures and excessive moisture. Mites, whiteflies, thrips, etc., love weak tender clones. Remove infested clones from the room. Cooler conditions, 65-78°F (18-25°C), slow mite and fungal spore reproduction and allow you to avert an infestation.

Do not use fertilizers on clones or seedlings.
Rooting Hormones
    Root-inducing hormones speed plant processes. When the stem of a cutting develops roots, it must transform from producing green stem cells to manufacturing undifferentiated cells and, finally, to fabricating root cells. Rooting hormones hasten growth of undifferentiated cells. Once undifferentiated, cells quickly transform into root cells. Three substances that stimulate undifferentiated growth include napthalenaecetic acid (NAA), indolebutyric acid (IBA) and 2, 4-dichlorophenoxyacetic acid (2, 3 DPA). Commercial rooting hormones contain one, two, or all of the above synthetic ingredients and often include a fungicide to help prevent damping-off.
    Rooting hormones are available in liquid, gel, or powder form. Liquid and gel types penetrate stems evenly and are the most versatile and consistent. Powdered rooting hormones adhere inconsistently to stems, penetrate poorly, spur uneven root growth, and yield a lower survival rate.

    Liquid rooting hormones can be mixed in different concentrations. Always mix the most dilute concentration for softwood cuttings. Apply any rooting hormone containing IBA only once. If exceeded in concentration or duration, IBA applications impair root formation. As soon as cuttings are taken, clones start dispatching rooting hormones to the wound. They