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

develop interveinal chlorosis.
    All foliage yellows and the leaf drop is severe.
    Treat deficiency by fertilizing with N or a complete N-P-K fertilizer. You should see results in four to five days. Fast-acting organic sources of nitrogen include seabird guano, fish emulsion, and blood meal. Growers also report excellent results by adding bio-fertilizers (see “Additives” page 285) to stimulate the uptake of nitrogen.
    Toxicity: An overdose of nitrogen will cause excessively lush foliage that is soft and susceptible to stress, including insect and fungal attacks. The stems become weak and they may fold over easily. The vascular transport tissue breaks down, and water uptake is restricted. In severe cases, leaves turn a brownish-copper color, dry, and fall off. Roots develop slowly, and they tend to darken and rot. Flowers are smaller and sparse. Ammonium toxicity is most common in acidic soils, while nitrate toxicity is more prevalent in alkaline soil.
    Progression of toxicity symptoms at a glance:
    Excessively lush, green foliage.
    Weak stems that fold over.
    Slow root development.
    Flowers become wispy.
    Leaves brown, dry, and fall off.
    Treat toxicity by flushing the growing medium of the affected plants with a very mild, complete fertilizer. Severe problems require that more water be flushed through the growing medium to carry away the toxic elements. Flush a minimum of three times the volume of water for the volume of the growing medium. Do not add more fertilizer that contains nitrogen for one week so the excess nitrogen in foliage can be used. If the plants remain excessively green, cut back on the nitrogen dose.

Beginning of N deficiency.

Progression of N deficiency.

Later stage of N deficiency.

Early stage of N overdose.

Later stage of N overdose.
Phosphorus (P) - mobile
    Practical Information: Cannabis uses the highest levels of phosphorus during germination, seedling, cloning, and flowering. Super Bloom fertilizers, designed for flowering, have high levels of phosphorus.
    Technical Information: Phosphorus is necessary for photosynthesis and provides a mechanism for the energy to transfer within the plant. Phosphorus–one of the components of DNA, many being enzymes and proteins–is associated with overall vigor, resin, and seed production. The highest concentrations of phosphorus are found in root-growing tips, growing shoots, and vascular tissue.
    Deficiency A lack of phosphorous causes stunted growth and smaller leaves; leaves turn bluish-green and blotches often appear. Stems, leaf stems (petioles), and main veins turn reddish-purple starting on the leaf’s underside. NOTE: The reddening of the stems and the veins is not always well pronounced. The leaf tips of older leaves turn dark and curl downward. Severely affected leaves develop large purplish-black necrotic (dead) blotches. These leaves later become bronzish-purple, dry, shrivel up, contort, and drop off. Flowering is often delayed, buds are uniformly smaller, seed yield is poor, and plants become very vulnerable to fungal and insect attack. Phosphorus deficiencies are aggravated by clay, acidic, and soggy soils. Zinc is also necessary for proper utilization of phosphorus.

Early stage of P deficiency.

Progression of P deficiency.

Later stage of P deficiency.
    Deficiencies are somewhat common and are often misdiagnosed. Deficiencies are most common when the growing-medium pH is above 7 and phosphorus is unable to be absorbed properly; the soil is acidic (below 5.8) and/or there is an excess of iron and zinc; the soil has become fixated (chemically bound) with phosphates.
    Progression of deficiency symptoms at a glance:
    Stunted and very slow-growth plants.
    Dark bluish-green leaves, often with dark blotches.
    Plants are smaller overall.
    When blotches overcome the leaf stem, the leaf turns bronzish-purple, contorts, and drops.
    Treat deficiency by lowering the pH to 5.5-6.2 in hydroponic units; 6 to 7 for clay soils; and 5.5-6.5 for potting soils so phosphorus will become available. If the soil is too acidic, and an excess of iron and zinc exists, phosphorous becomes unavailable. If you are growing in soil, mix a complete fertilizer that contains phosphorus into the growing medium before planting. Fertigate with an inorganic, complete hydroponic fertilizer that contains phosphorus. Mix in the organic nutrients–bat guano, steamed bone meal, natural phosphates, or barnyard manure–to add phosphorus to soil. Always use finely ground