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

organic components that are readily available to the plants.
    Toxic signs of phosphorus may take several weeks to surface, especially if excesses are buffered by a stable pH. Marijuana uses a lot of phosphorus throughout its life cycle, and many varieties tolerate high levels. Excessive phosphorus interferes with calcium, copper, iron, magnesium, and zinc stability and uptake. Toxic symptoms of phosphorus manifest as a deficiency of zinc, iron, magnesium, calcium and copper; zinc is the most common.
    Treat toxicity by flushing the growing medium of affected plants with a very mild and completefertilizer. Severe problems require more water to be flushed through the growing medium. Flush a minimum of three times the volume of water for the volume of the growing medium.
Potassium (K) - mobile
    Practical Information: Potassium is used at all stages of growth. Soils with a high level of potassium increase a plant’s resistance to bacteria and mold.
    Technical information: Potassium helps combine sugars, starches, and carbohydrates, which is essential to their production and movement. It also is essential to growth by cell division. It increases the chlorophyll in the foliage and helps to regulate the stomata openings so plants make better use of the light and air. Potassium is essential in the accumulation and translocation of carbohydrates. It is necessary to make the proteins that augment the oil content and improve the flavor in cannabis plants. It also encourages strong root growth and is associated with disease resistance and water intake. The potash form of potassium oxide is (K 2 O).
    Deficiency Potassium-starved plants initially appear healthy. Deficient plants are susceptible to disease. Symptoms include the following: older leaves (first tips and margins, followed by whole leaves) develop spots, turn dark yellow, and die. Stems often become weak and sometimes brittle. Potassium is usually present in the soil, but it is locked in by high salinity. First, leach the toxic salt out of the soil and then apply a complete N-P-K fertilizer. Potassium deficiency causes the internal temperature of the foliage to climb and the protein cells to burn or degrade. Evaporation is normally highest on leaf edges, and that’s where the burning takes place.
    The progression of the deficiency symptoms at a glance:
    Plants appear healthy with dark green foliage.
    The leaves lose their luster.
    Branching may increase, but the branches are weak and scrawny.
    Leaf margins turn grey and progress to a rusty-brown color, and then curl up and dry.
    Yellowing of the older leaves is accompanied by rust-colored blotches.
    The leaves curl up, rot sets in, and the older leaves drop.
    The flowering is retarded and greatly diminished.
    Treat deficiency of potassium by fertilizing with a complete N-P-K fertilizer. Occasionally, a grower will add potassium directly to the nutrient solution. Organic growers add potassium in the form of soluble potash (wood ashes) mixed with water. Be careful when using wood ash, the pH is normally above 10. Use a pH-lowering mix to bring the pH to around 6.5 before application. Foliar feeding to cure a potassium deficiency is not recommended.
    Toxicity occurs occasionally and is difficult to diagnose because it is mixed with the deficiency symptoms of other nutrients. Too much potassium impairs and slows the absorption of magnesium, manganese, and sometimes zinc and iron. Look for signs of toxic-potassium buildup when symptoms of magnesium, manganese, zinc, and iron deficiencies appear.
    Treat toxicity by flushing the growing medium of affected plants with a very mild and complete fertilizer. Severe problems require that more water be flushed through the growing medium. Flush with a minimum of three times the volume of water for the volume of the growing medium.

Early stage of K deficiency.

Progression of K deficiency.

Later stage of K deficiency.
Secondary Nutrients
    The secondary nutrients–magnesium, calcium, and sulfur–are also used by the plants in large amounts. Rapid-growing indoor marijuana crops are able to process more secondary nutrients than most general-purpose fertilizers are able to supply. Many growers opt to use high quality two- and three-part hydroponic fertilizers to supply all necessary secondary and trace elements. But be careful, these three nutrients may be present in high levels in the ground water. It is important to consider these values when adding nutrient supplements. If growing