Home Cultivation Why Your Cannabis Plant Needs Magnesium

Why Your Cannabis Plant Needs Magnesium

Don't Ignore The Macro Effects of So-Called Micronutrients


Your Cannabis Gets a Huge Boost From Magnesium

Magnesium (Mg) is an activator of enzymes as well as an essential building block of chlorophyll, helping to capture photons and harness energy from the sun outdoors or grow lamps indoors to power the amazing food factory bio-machinery of plants. There are some striking, but superficial, similarities between the molecular structure of hemoglobin, built around an iron atom, and chlorophyll, built around an atom of magnesium. Beware of the goofy religiosity gripping some folks who preach the latest snake oil fad diet gospel of chlorophyll as a miraculous healing super-food, but I digress.

Sulfur, calcium and magnesium are often referred to as “secondary nutrients”, rather than micronutrients, because they are so important to the well being of plant life and required in much greater quantities than the true micros. Both calcium and magnesium can be found in dolomite lime, which should be amended to the soil with the understanding that it may take up to a year for the mineralized nutrients to become available to plants in soluble form. Dolomite lime is also used to raise the pH levels of soil. Most soils in California start out slightly basic (above 7.0) and contain an abundance of mineralized calcium and magnesium, but over time, organic fertilizers and acid rain can lower the pH to the point of locking up certain nutrients, requiring adjustment.

An important tell-tale visual indication that your Cannabis is suffering from a magnesium deficiency is that lower yellowing leaves retain a contrasting green coloring in the veins even as edges brown, curl and die back. The yellowing is known as chlorosis. Magnesium is mobile in plants and when insufficient magnesium is available to the roots, a plant will destroy the chloroplasts in older leaves in order to borrow and transport the magnesium up to the crown for newer growth. When the green component of the leaf (chloroplasts containing chlorophyll) becomes scarce, the underlying shades of yellow and even white begin to show through.

Healthy, robustly growing Cannabis will eventually deplete even the richest organically amended soil which started the season with generous helpings of compost. Excessive rains or irrigation can leach magnesium out of the soil, washing away this valuable nutrient. Additionally, efficient magnesium uptake can be muted by the presence of high levels of potassium or very low pH.

Epsom salts (magnesium sulfate) can be obtained cheaply and in bulk at your neighborhood drug store chain to keep your Cannabis mean and green, as inexpensive as around three bucks for four pounds. Irrigate the plant roots with a solution of 1 tablespoon per gallon at the first signs of deficiency. Foliar feeding can also be beneficial.

Any advice and opinions about the cultivation of Cannabis offered by Bruce N. Goren are his own and do not represent the University of California or the Master Gardener Program.