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Cannabis has a greater need for magnesium than other plants. Indoor growers especially must remain vigilant for the signs of magnesium deficiency. Most basic nutrient products from your hydroponics supply store have the N-K-P covered, but micronutrients, like magnesium, are equally as important (and sometimes overlooked).

Cannabis magnesium deficiencies can strike both soil-based and hydroponic growers throughout all stages of the growth cycle. Careful attention to the signs of magnesium deficiency can help you catch this issue and others (ex: calcium and potassium) before damaging the flower. Among the secondary nutrients, magnesium is the most crucial for that plant’s development and growth after the three primary nutrients. Without magnesium, plants may not flourish well. How can you spot cannabis magnesium deficiency, and how will you treat that? Keep reading to gain information on this topic. 

After the three primary nutrients (nitrogen, potassium, and phosphorus), magnesium is the most crucial secondary nutrient for the healthy growth and development of cannabis plants. Without it, plants wither, fail to thrive, and eventually die. What does a cannabis plant with magnesium deficiency look like, and what can be done to help it recover? Help is at hand!

The Role of Magnesium in Growing Cannabis

Cannabis is a nutrient hog and based on the current understanding, requires more magnesium than other commonly cultivated crops. Without magnesium, cannabis (and all plants) cannot feed itself through photosynthesis.

Magnesium is literally at the core of the plant’s energy production. It sits squarely in the center of the chlorophyll molecule. Without magnesium, cannabis will stumble in producing that vibrant green color and fail to provide enough food (energy) for healthy growth.

Magnesium is a mobile nutrient, meaning the plant can move the nutrient from old leaves into new leaves. If not caught early, your plants might begin making this rapid movement of magnesium, killing all older, lower leaves.

Read this too: How to Increase Cannabis Resin Production ?

How can magnesium deficiencies in cannabis plants be identified?

Cannabis Nutrients

As the primary ‘building block’ of chlorophyll, magnesium is what gives it, and therefore the plant itself, a healthy bright green color. The first and most easily identified sign of cannabis magnesium deficiency are the leaves showing a worrying fade of green to pale green to yellow. This is known as chlorosis. Although other problems also cause chlorosis, cannabis magnesium deficiency shows up first around the edges and in between the veins on the leaves, rather than all over them or from the stems outwards or tips inwards.

The first leaves to show these signs will be the oldest ones and those closest to the bottom of the plant (often, these are the same ones). This is caused by the plant withdrawing magnesium from these leaves to send it to the newer ones to keep itself alive (in much the same way the human body pulls blood away from the extremities in cold weather to keep the vital organs warm). The leaves might also start to feel crunchy and dry, although it is not advisable to wait until this happens before starting treatment!

How to Fix a Magnesium Deficiency in Soil?

Although cannabis magnesium deficiency is most common with soilless growers, there are times when soil-bound growers become susceptible to this nutrient issue as well. Under certain conditions, an imbalance with other nutrients can lock cannabis out of micronutrient absorption.

Elevated levels of other nutrients, like potassium and calcium, may trigger the nutrient lockout of magnesium. Other environmental influences can also impact nutrient absorption, most critically pH level.

Once you’ve identified the issue, test the soil for pH, and adjust as needed to fall back within the ideal 6.0 to 7.0 pH with a water flush. Once flushed, assess the nutrients you have used to better understand the magnesium supply.

Epsom salt is the most common way to apply straight magnesium to your growth, but it must be diluted into the water at a 20-25 ppm ratio. Dolomite is a combination of calcium and magnesium, also useful for immediate correction. 

With a market full of cannabis-specific nutrients catering to all types of substrates and stages of growth, it may be time to refresh your current supply. If you’ve been mixing nutrients or adapting non-cannabis varieties, consider a switch to improve magnesium uptake in your cannabis plants. 

Tips to avoid cannabis magnesium deficiency

Soil growers should consider potting from smaller containers filled with lightly fertilized soil to large containers with a time-release fertilizer/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 growth. 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 works to treat a cannabis magnesium deficiency. Roughly as well as a 19th-century barber performing surgery.

We hope that this article has been informative about curing cannabis magnesium deficiency.


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