Sulfur (S)

Marijuana Horticulture

by Jorge Cervantes

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.

Sulfur is an essential building block of many hormones and vitamins, including vitamin B1. 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 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 gypsym (calcium sulfate) and settle as residue to the bottom of the tank.

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 detailed scientific experiments with nutrients, says, “We have repeatedly noticed that the symptoms were most obvious in the older leaves.” Sulfur deficiency resembles a nitrogen deficiency. Acute sulfur deficiency causes elongated stems that become woody at the base.

Sulfur deficiency occurs indoors when the pH is too high or when there is excessive calcium present and available.

Acute deficiency causes more and more leaves to develop purple leaf stems and yellow leaves.

Treat deficiency by fertilizing with a hydroponic fertilizer that contains sulfur. Lower pH to 5.5 to 6. Add inorganic sulfur to a fertilizer that contains magnesium sulfate (Epsom salts). Organic sources of sulfur include mushroom composts and most animal manures. Make sure to apply only well-rotted manures to avoid burning the roots.

An excess of sulfur in the soil causes no problems if the EC is relatively low. At a high EC, the plants tend to take up more available sulfur which blocks uptake of other nutrients. Excess sulfur symptoms include overall smaller, dark green foliage. Leaf tips and margins could discolor and burn when severe.

Treat toxicity by flushing the growing medium of affected plants with a very mild and complete fertilizer. Check the pH of the drainage solution. Correct the input pH to 6. 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.