Updated: Dec 15, 2020
One of the most common deficiencies that cannabis growers experience is magnesium deficiency. Magnesium is a secondary nutrient and it is needed in all stages of the plant's life.
Magnesium deficiency is a mobile deficiency. That means the problem starts out at the bottom of the plant and slowly escalates up the plant until the plant dies. Magnesium deficiency usually becomes apparent once the plant is about a month old - so It doesn't tend to happen right away. Magnesium deficiency is far more common when growing cannabis indoors vs growing cannabis outdoors. Early stage magnesium deficiency starts off as a yellowing of the leaves between the veins. It then slowly starts to climb up the leaves and while it's climbing, some of the first affected leaves will develop rusty-looking spots. But don't get confused. The rusty-looking spots are actually a sign of calcium deficiency. When a plant is deficient in magnesium, it will often times also become deficient in calcium. We will talk more about calcium deficiency in a different article.
Eventually, when the leaves get really bad, they start to die and they curl upward. After that, the leaf just dies and falls off. How do you fix magnesium deficiency in cannabis plants? Add in a magnesium supplement. Here are the top magnesium supplements on the market today:
When feeding your plant a magnesium supplement, make sure the pH is in the correct range. If the pH is not in the correct range, the plant may not be able to uptake the nutrients in the growing medium and a nutrient lockout may occur. Once the problem is fixed, yellowing will stop advancing up the plant and growth will resume as normal.
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