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

stunted. Deficiencies are worst in acidic soils.
    Toxicity: Excess is uncommon in marijuana gardens. An excess of molybdenum causes a deficiency of copper and iron.
Silicon - (Si)
    Practical Information: Silicon is readily available in most soils, water, and as far as I know, it does not cause cannabis any complications due to deficiencies or excesses.
    Technical Information: Silicon is absorbed by the plants as silicic acid. Silicon assists in keeping iron and manganese levels consistent. It is found mainly in the epidermal cell walls where it collects in the form of hydrated amorphous silica. It also accumulates in the walls of other cells. Adequate and soluble silicon guarantees stronger cell walls that resist pest attacks and increase heat and drought tolerance.
    Deficiency: A lack of silicon has been proven to decrease yields of some fruits and cause new leaves to deform.
    Excess: Never heard of a problem.
    NOTE: Pests and diseases have a difficult time penetrating the plants that are sprayed with a silicon-based repellent/insecticide.
Nickel - (Ni)
    Enzymes require nickel to break down and use the nitrogen from the urea. It is also essential to iron absorption. Seldom deficient and subtly mixed with other nutrient deficiencies, most commonly nitrogen.

Fertilizers show the N-P-K in big letters on the front of the package.
Sodium - (Na)
    This is one of the problem elements. A little bit will go a long way! Sodium is taken up by the roots very quickly and in small amounts (50 ppm). It can block enough other nutrients causing severe deficiencies to result. When mixed with chlorine, it turns into table salt, which is the worst possible salt to put on the plants. Be very careful to measure your input water to ensure that it contains less than 50 ppm sodium. The less sodium in the solution, the better.
Fluoride - (F)
    Some water systems are abundant with fluoride. If concentrated, fluoride can become toxic. I have yet to see fluoride toxicity or deficiency cause problems in an indoor grow room.
Fertilizers
    The goal of fertilizing is to supply the plants with the proper amounts of nutrients for vigorous growth, without creating toxic conditions by overfertilizing. A 2-gallon (8 L) container full of rich, fertile potting soil will supply all the necessary nutrients for the first month of growth, but the development might be slow. After the roots have absorbed most of the available nutrients, more must be added to sustain vigorous growth. Unless fortified, soilless mixes require fertilization from the start. I like to start fertilizing fortified soilless mixes after the first week or two of growth. Most commercial soilless mixes are fortified with trace elements.
    Marijuana’s metabolism changes as it grows and so do its fertilizer needs. During germination and seedling growth, intake of phosphorus is high. The vegetative growth stage requires larger amounts of nitrogen for green-leaf growth, and phosphorus and potassium are also necessary in substantial levels. During this leafy and vegetative growth stage, use a general purpose or a grow fertilizer with high nitrogen content. In the flowering stage, nitrogen takes a backseat to potassium, phosphorus, and calcium intake. Using a super bloom fertilizer with less nitrogen and more potassium, phosphorus, and calcium promotes fat, heavy, dense buds. Cannabis needs some nitrogen during flowering, but very little. With no nitrogen, buds do not develop to their full potential.
    Now we come to the confusing part about the guaranteed analysis of commercial fertilizer mixes. Federal and state laws require nutrient concentrations to appear prominently on the face of the fertilizer packages, even though the accuracy of the values is dubious.
    Do you think the N-P-K numbers on the label give the percentages of nitrogen, phosphorous, and potassium? Well, yes and no. The scale measures nutrients with different scales. Nitrogen is listed as total combined elemental. Most hydroponic fertilizers break nitrogen into slow-acting nitrate (NO 3 ) and ammonium (NH 4 ). Phosphoric anhydride (P 2 O 5 ) is listed as the form of phosphorus, but this figure understates phosphorus content by 44 percent. It gets worse! The balance (56 percent) of the phosphorus molecule is comprised of oxygen. Twenty percent P 2 O 5 is 8.8 percent actual phosphorous. Potassium (K) is listed in the potash form of potassium oxide (K 2 O) of which 83 percent of the stated value is actually elemental potassium.
    The