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

inhibit calcium uptake. Signs of excess magnesium are described below.
    Toxicity: Magnesium toxicity is rare and difficult to discern with the naked eye. If extremely toxic, the magnesium develops a conflict with other fertilizer ions, usually calcium, especially in hydroponic nutrient solutions. The toxic buildup of magnesium in soil that is able to grow marijuana is uncommon.
Calcium (Ca) - immobile
    Practical Information: Cannabis requires nearly as much calcium as other macronutrients. Avert deficiencies in the soil and in most soilless mixes by adding fine dolomite lime or using soluble-hydroponic fertilizers containing adequate calcium.
    Technical Information: Calcium is fundamental to cell manufacturing and growth. Calcium is necessary to preserve membrane permeability and cell integrity, which ensures proper flow of nitrogen and sugars. It stimulates enzymes that help build strong cell and root walls. Cannabis must have some calcium at the growing tip of each root.
    Deficiency of calcium is somewhat uncommon indoors, but not uncommon in fiber hemp. Frequently, plants can process more calcium than is available. It also washes out of the leaves that are sprayed with water. Deficiency signs may be difficult to detect. They start with weak stems, very dark green foliage, and exceptionally slow growth. Young leaves are affected, and they show the signs first. Severe calcium deficiency causes new, growing shoots to develop yellowish to purple hues and to disfigure before shriveling up and dying; bud development is inhibited, the plants are stunted, and harvest is diminished. Growing tips could show signs of calcium deficiency if the humidity is maxed out. At 100 percent humidity, the stomata close, which stops the transpiration to protect the plant. The calcium that is transported by transpiration becomes immobile.
    Treat deficiencies by dissolving one-half teaspoon of hydrated lime per gallon of water. Water the deficient plants with calcium-dosed water as long as the symptoms persist. Or use a complete hydroponic nutrient that contains adequate calcium. Keep the pH of the growing medium stable.
    Progression of deficiency symptoms at a glance:
    Slow growth and young leaves turn very dark green.
    New growing shoots discolor.
    New shoots contort, shrivel, and die.
    Bud development slows dramatically.
    Toxicity is difficult to see in the foliage. It causes wilting. Toxic levels also exacerbate deficiencies of potassium, magnesium, manganese, and iron. The nutrients become unavailable, even though they are present. If excessive amounts of soluble calcium are applied early in life, it can also stunt the growth. If growing hydroponically, an excess of calcium will precipitatewith sulfur in the solution, which causes the nutrient solution to suspend in the water and to aggregate into clumps causing the water to become cloudy (flocculate). Once the calcium and sulfur combine, they form a residue (gypsum Ca(SO 4 ).2(H 2 O)) that settles to the bottom of the reservoir.
Sulfur (S) - immobile
    Practical Information: Many fertilizers contain some form of sulfur, and for this reason, sulfur is seldom deficient. Growers avoid elemental (pure) sulfur in favor of sulfur compounds such as magnesium sulfate. The nutrients combined with sulfur mix better in water.
    Technical Information: Sulfur is an essential building block of many hormones and vitamins, including vitamin B 1 . Sulfur is also an indispensable element in many plant cells and seeds. The sulfate form of sulfur buffers the water pH. Virtually all ground, river, and lake water contains sulfate. Sulfate is involved in protein synthesis and is part of the amino acid, cystine, and thiamine, which are the building blocks of proteins. Sulfur is essential in the formation of oils and flavors, as well as for respiration and the synthesis and breakdown of fatty acids. Hydroponic fertilizers separate sulfur from calcium in an “A” container and a “B” container. If combined in a concentrated form, sulfur and calcium will form crude, insoluble gypsum (calcium sulfate) and settle as residue to the bottom of the tank.
    Deficiency: Young leaves turn lime-green to yellowish. As shortage progresses, leaves yellow interveinally and lack succulence. Veins remain green, and leaf stems and petioles turn purple. Leaf tips can burn, darken, and hook downward. According to literature, youngest leaves should yellow first. But Mauk from Canna Coco in the Netherlands, who has conducted