Boron (B)

Marijuana Horticulture

by Jorge Cervantes

Usually causes no problems, but boron must be available during the entire life of a pant.

Boron deficiencies seldom occurs indoors. Boron is still somewhat of a biochemical mystery. We know that boron helps with calcium uptake and numerous plant functions. Scientists have collected evidence to suggest boron helps with synthesis, a base for the formation of the nucleic acid (RNA uracil). Strong evidence also supports boron’s role in cell division, differentiation, maturation, and respiration as well as a link to pollen germination.

Stem tip and root tip grow abnormally. Root tips often swell, discolor, and stop elongating. Growing shoots look burned and may be confused with a burn from being too close to the HID light. First leaves thicken and become brittle, top shoots contort and/or turn dark, which is later followed by progressively lower-growing shoots. When severe, growing tips die, and leaf margins discolor and die back in places. Necrotic spots develop between leaf veins. Root steles (insides) often become mushy – perfect hosts for rot and disease. Deficient leaves become thick, distorted, and wilted with chlorotic and necrotic spotting.

Treat boron-deficient plants with one teaspoon of boric acid per gallon of water. You can apply this solution as a soil drench to be taken up by the roots, or apply hydroponic micronutrients containing boron. Hydroponic gardeners should keep boron dosage below 20 parts per million (ppm), because boron quickly becomes toxic if it is concentrated in the solution.

Leaf tips yellow first, and as the toxic conditions progress, leaf margins become necrotic toward the center of the leaf. After the leaves yellow, they fall off. Avoid using excessive amounts of boric acid-based insecticides.