By Steven Voser

Browse Deficiencies
Browse Deficiencies
Browse Deficiencies


Magnesium deficiency is the definition of a bottom to top nutrient imbalance in cannabis. Growers will first notice unhealthy looking lower growth. It’s the oldest and lowest leaves that will signal the advance of a magnesium deficiency. In the beginning, bottom leaves will yellow and the tips will dry out into a crunchy brown.

Unfortunately, magnesium deficiency is mobile, so it will spread up the plant if left unchecked. As the deficiency spreads to the shoots, they will turn purple and leaf chlorosis will accelerate. Grower reaction time, as always, will be the defining factor. Don’t mistake magnesium deficiency for nitrogen starvation.

Probably the biggest mistake novice growers make is rushing to apply a quick fix by increasing nutrient doses. In fact, this will likely lead to nutrient lockout. No matter the growth stage or medium, yellow leaves and brown spots starting from the bottom are a red flag for magnesium deficiency. Micronutrient deficiencies always start in the root zone; magnesium deficiency is no exception. The problem must be remedied at the source. More on that a little later.

Magnesium deficiency plant


Coco coir is a great growing medium, but it can cause problems for growers concerning micronutrient uptake. Magnesium, along with calcium and iron, is one of the three micronutrients cannabis plants cropped in coco have difficulty absorbing.

Hydroponic growers that let the pH of the nutrient solution slip to 5.0 or below will likely experience magnesium deficiency. Water with too low a pH in the reservoir is a recipe for micronutrient lockout. Indoor soil growers often encounter magnesium deficiency for two reasons. The first is over-watering the soil. Roots in soggy soil just can’t access the nutes.

However, the second is more difficult to detect. Growers that use lightly fertilised soil and liquid nutrients lacking in trace elements can unexpectedly get hit with a magnesium deficiency during mid-late bloom. As the marijuana plant matures, roots essentially drink up all the micronutrients in the medium. Without adequate supplementation, magnesium deficiency strikes.


Solving a magnesium deficiency should begin with a flush of 6.0pH water. This should work fine for all substrates. Next, you need to prepare a feed with the optimal pH for your growing medium. (Soil: 6.0-6.5, Coco: 6.0 and Hydro: 5.5-6.0). In addition to the usual brew of nutes, add a high-quality, cannabis-specific magnesium supplement.

magnesium deficiency cannabis leaf


As above, rinse out the substrate. But instead of adding a supplement, a better long term solution is to consider a nutrients upgrade. Specific nutrient lines customised to soil, coco or hydro grow styles make life a whole lot easier. Premier brand base-nutes are formulated with the complete macro and micronutrients needed for cannabis cultivation.


Soil growers should consider potting up from smaller containers filled with lightly fertilised soil to large containers with a time-released fertiliser/soil mix. After a few weeks of vegetative growth, roots will be hungry for nutes and more fertile soil will save you money on bottles of liquid alternatives.

Investing in a high-quality growing medium and cannabis-specific nutrients is the best way to avoid troubleshooting deficiencies later during the grow. Finally, we cannot finish without a word on Epsom salts. To be honest, recommending them would be cannabis quack-doctoring. Let’s just say it kind of works to treat a magnesium deficiency. Roughly as well as a 19th-century barber performing surgery.

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