Tips to avoid mineral deficiencies when growing cannabis

Published Apr 20, 2019 09:20 a.m. ET
AP Photo/Jae C. Hong

Vitamins and minerals are two necessary nutrients for a healthy crop. A deficiency of any essential nutrient can pose a significant risk to your plant and even kill it if certain symptoms aren’t noticed in time. While there are numerous ways to treat a deficiency in cannabis plants, the best tactic to take is avoiding the chances of it happening beforehand rather than trying to do damage control after the fact because by than harm will have already occurred. Here we will show you the best nutrients for weed that can be used to avoid some of the most common deficiencies growers are likely to experience.


Iron is one of the most necessary nutrients for weed, as it works directly with the enzyme production process. When the iron levels within a cannabis plant run low,it will affect both leaf respiration and the pigmentation of the leaves.

Iron deficiency weed symptoms: When there are iron deficiencies in a cannabis plant the first symptom is usually a yellowing of the leaves that are located highest on the plant. If you find you have a higher than 7.0 PH value in the dirt than the culprit the soil that is hindering the plant'sability to absorb a sufficient amount of iron through its roots. The leaves will slowly turn yellow leaving behind bright green colored veins.

How to avoid an iron deficiency: When preparing the soil to grow marijuana in, it is best to add a natural iron material such as granular or powdered chelated iron. There are other options like placing a small copper pipe in the pot or dirt next to a plant, but pieces of metal can be sharp and possibly damaging so be careful if you choose that route.  


Magnesium is one of the most utilized nutrients by cannabis throughout every stage of development, and it is needed in fairly substantial quantities. Magnesium works to encourage a plants ability to absorb nutrients from sunlight which is then made into precious carbohydrates and sugars that the plant feasts off of. Cannabis plants absorb 90% of their magnesium through the soil, and can become deficient is the material it is grown in is insufficient. Sometimes the magnesium present may be enough, but simply has yet to grow the necessary microbial life needed to convert it into a form the plant can absorb.

Magnesium deficiency weed symptoms: Soil PH of less than 5.0 can often be one of the first indicators of a problem arising. The symptoms of this deficiency will show themselves in the lower portions of the plant and on the oldest leaves.

How to avoid a magnesium deficiency: Two of the most commonly used soil amendments to avoid a magnesium deficiency are lime, and epsom salts. You will only need a small amount, approximately one teaspoon of either per 2-gallon pot. Both will slowly feed this essential cannabis nutrient to your plant and help you to avoid a deficiency in the future.


Calcium is what is called a primary cannabis nutrient because so much of it is required throughout every stage of growth. It helps to strengthen the cell walls of the plant'sroot system as it forms, and stimulates the decomposition process of the soil around it which in turn allows the plant much faster access to many other essential nutrients.  

Calcium deficiency weed symptoms: Since a lack of calcium can affect the growth of the entire plant, one of the first visible symptoms is a dramatic slow in growth. Once a calcium deficiency gets too out of control, new growth will completely die off and turn yellow or brown.

How to avoid a calcium deficiency: Often calcium deficiencies are caused by acidic soil. To avoid having to deal with a deficiency altogether consider using gypsum or limestone. Both can be purchased in whole or granulated form making them easy to add to any homemade super soil recipe. Only ½ of a teaspoon of either one is needed to support a 2-gallon pot, and the fresh stream of nutrients will continue to flow for 6-8 months after.


Phosphorus is a macro-nutrient since it is needed in large amounts to maintain the metabolism of a cannabis plant. Phosphates are delivered through the ground after they have been consumed by various life forms in the surrounding soil. This cannabis nutrient is most essential during germination, root establishment, cloning, and the flowering stages of life.  

Phosphorus deficiency weed symptoms: When phosphorus is in short supply, a marijuana plant will force it into the newer and healthier leaves. At which point the older portions of the plant will begin to turn yellow which is a process called chlorosis. If this deficiency lasts too long, it will eventually make its way through all of the leaves slowly killing the plant.

How to avoid a phosphorus deficiency: Phosphorus is one of the easiest and most natural nutrients to use to fertilize your plant, making this deficiency also relatively simple to avoid. High levels of phosphorus are contained within a healthy compost pile as long as you are putting the right things into it. Bananas, eggshells, coffee grinds, and ash can all be used either combined or added directly to the soil in small amounts. If you want to add some to a pre-potted plant,you can sprinkle a teaspoon of any of the above, or place a slice of banana peel on top of the dirt, and your plant will receive a consistent flow of phosphorus for several months.


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