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David Rhodes

David has been working in the cannabis industry for the past 17 years with experience working overseas in Amsterdam as a budtender for 5 years! Learn More About David!

Latest Update on January 26th, 2023: Magnesium shortage in cannabis is not a rare occurrence. If you cultivate cannabis, there’s a chance you might face this issue at a certain point. This lack of magnesium results in the leaves turning yellow and stems getting darker.

Magnesium Deficiency In Cannabis:

Common causes of magnesium deficiency include poor soil pH and overwatering.

magnesium deficiency in cannabis

Using optimal soil pH and adequate watering of your cures magnesium deficiency. Another way of combating this deficiency is by using magnesium fertilizer and supplements. Identifying magnesium deficiency in cannabis can be difficult because it looks similar to other nutrient deficiencies such as potassium and nitrogen.

What Is The Role Of Magnesium In Cannabis?

Magnesium is considered a secondary nutrient for cannabis growth and is extremely important. It is important to make sure that your plants have optimal levels of magnesium for proper growth.

Mostly needed in the leaves, magnesium plays a big role in all stages of growth of your cannabis plant.

Here are the different roles of magnesium in cannabis;

Converting Light Into Energy For Fast Growth

Magnesium plays an important role in converting light into energy. Cannabis plants need energy to grow and magnesium plays a huge role in encouraging the absorption of light by the plant.

By absorbing light through the leaves, a plant creates sugars and carbohydrates needed for growth.

The Vegetative Stage For Growth

At the vegetative stage of plant growth and roots begin to grow. When the roots are growing, magnesium is necessary to encourage growth.

Bud Growth During Flowering

Magnesium is responsible for bud growth during the flowering process. Your plants need to have enough flowering nutrients and magnesium is one of them. Since magnesium helps turn light into energy, deficiency can affect bud growth and delay the flowering process.

Give Cannabis Green Color

Without magnesium, cannabis plants turn yellow. It is responsible for capturing sunlight in plants. Chlorophyll and magnesium absorb sunlight which is responsible for the green color in leaves.

How To Spot Magnesium Deficiency In Cannabis

The following signs indicate magnesium deficiency in cannabis;

Yellowing Of Leaves

Yellowing of leaves is probably the first sign of magnesium deficiency in cannabis. It starts with the older leaves and progresses to the fresher ones.

magnesium deficiency in weed

As aforementioned, the reason leaves turn yellow is because magnesium helps absorb sunlight with the help of chlorophyll to give leaves a green color.

The yellowing that happens due to lack of magnesium is different. It starts at the outer corner of the leaves and starts moving inwards. it resembles a tie and dye pattern.

In some instances, the leaves might turn yellow and the veins remain green. In other cases, they might turn brown. If you notice the browning of the leaves alongside yellowing, it means the plant has other nutritional deficiencies.

Dry And Brittle Leaves

Magnesium deficiency can also lead to Chloris that not only makes cannabis leaves lose their green color but also become brittle and dry. Lack of magnesium lowers sugars and carbohydrates responsible for making the plant strong and healthy. This can also look like rust spots on your cannabis plant.

mg deficiency in weed plants

The plant starts “starving” of nutrients causing leaves to dry and fall off.

Red And Purple Stems

Red and purple stems are common when dealing with magnesium deficiency. Other causes of red stems in your cannabis plant include ”sun tan,” genetics, temperature fluctuations, stress, and wrong pH.

Studded Growth

Studded growth in cannabis plants is a sign of magnesium deficiency. Magnesium is an important nutrient that is responsible for making food for the plant.

Sugars and carbohydrates for plant growth are made using magnesium. If your plant is low in magnesium it’ll experience slow growth which can lead to late harvest and poor yields. That being said, stunted growth can also be caused by many other issues such as a pest issues like spider mites.

Unhealthy Looking Plant

If your cannabis plant looks unhealthy generally, then it might be due to magnesium deficiency. Some of the things that characterize a healthy plant include the right size, strong stems, and green color.

What Causes Magnesium Deficiency In Cannabis?

Some of the common causes of magnesium deficiency in cannabis include;

Using The Wrong Type Of Soil

The type of soil you use to grow cannabis might cause magnesium deficiency. This is especially true when growing your plants outdoors.

You can experience magnesium deficiency when you have soil pH issues. A pH below 5 is optimum for cannabis growth and it is the best for supporting magnesium.

If the soil pH is higher or lower, then you’re likely to experience problems when growing cannabis.

Overwatering The Plant

As aforementioned, overwatering a cannabis plant causes magnesium deficiency. Only water the plant when the soil is dry. Overwatering neutralizes pH and makes it difficult to support magnesium.

If you keep overwatering your plant, you’ll flush out all nutrients including magnesium.

Using The Wrong Type Of Water

The water that you use to irrigate your cannabis plant is important. It is advisable to use water that has magnesium. Using water that has been filtered using reverse osmosis is discouraged.

How To Fix Magnesium Deficiency In Cannabis

The process of fixing magnesium deficiency in cannabis is systematic. It is advisable to do it one step at a time to get the best results. Unfortunately, many cannabis growers think pumping nutrients into the plant is the solution.

Sometimes the main problem is poor absorption of magnesium. If this is the case, ensure you fix the issue first.

Here are some steps on fixing magnesium deficiency in cannabis;

Wash Out All The Nutrients

The first step is to wash out all the nutrients. This step requires patience because you have to keep irrigating the cannabis plant. Washing out nutrients is important before introducing new nutrients into the plant.

wash out all the nutrients

Irrigating will dilute the plant and this will help you get rid of the primary and secondary nutrients needed by the plant.

Replenish The Nutrients

Once you have washed out all the nutrients it is time to replenish them. You can do that by using fertilizer or a supplement. Replenishing the nutrients after washing them out will allow better absorption.

It is the best way to make sure that all the nutrients are absorbed and not blocked. Depending on the type of farming that you are doing a fertilizer or a supplement will be okay.

Continue Watering The Plant

After you have used fertilizer or supplement it is time to continue watering the plant. It will help with growth and you can start seeing changes quickly.

Always remember not to overwater the plant because this can lead to washing out all the nutrients once again. Always stick to a watering schedule.

You can always water the plant once the soil becomes dry if you are not sure how to go about it.

Magnesium Nutrient Lockout

Magnesium nutrient lockout is common in cannabis plants. It occurs when magnesium is available in the soil but cannot be absorbed by the plant. This nutrient lockout can happen when the soil has an excess of one of the minerals like calcium.

magnesium lockout cannabis

When calcium is high in your soil then it can prevent the absorption of magnesium. Here are some of the causes of magnesium lockout in the cannabis plant and their solution:

Chemical fertilizer with high salt – if the chemical fertilizers that you are using have a high salt intake they can affect the absorption of magnesium nutrients.

The best way to use fertilizers that are good in quality. We have fertilizers with the right balance of salt and they are effective.

Excess of one nutrient – balancing out nutrients is important when growing cannabis. You need to have every nutrient in your soil for optimal growth.

For instance, if you have more calcium than magnesium then it is likely to lockout magnesium absorption.

Poor soil PH – the PH of your soil is an important factor. If your soil is too acidic or too alkaline then it might be difficult to absorb minerals.

In case you are not sure of your soil PH make sure that you do some testing. It will help to determine what to do so that you can balance out the PH. Balancing out the PH can help you encourage absorption.

Magnesium Toxicity In Cannabis

The deficiency of magnesium in cannabis can be detrimental to plant growth. The same case applies to toxicity in cannabis. It is important to have optimal levels of the nutrient so that you can encourage the growth of the plants.

In some rare cases, magnesium toxicity occurs. However, slightly higher levels of magnesium do not affect cannabis growth in adverse ways.

When the toxicity is too much, the presence of magnesium can lock out the absorption of calcium. It is not uncommon to see that your plant has started experiencing problems associated with calcium deficiency.

The first thing that you will notice is that levels start shrinking.

How To Fix Magnesium Toxicity In Cannabis

It is possible to fix magnesium toxicity in cannabis. It can be done by flushing out the nutrients. This is done by over-watering the plant for some time.

Overwatering will help you to eliminate toxicity so that you can start feeding your plant with magnesium according to the recommended levels. When fixing magnesium toxicity you can use the supplement.

It will help to know exactly how much you need to prevent toxicity.


Is there a difference between calcium and magnesium deficiency in cannabis?

Calcium and magnesium are both important nutrients needed for the growth of the cannabis plant. However, the deficiencies manifest differently. In calcium deficiency, the leaves start to curl while in magnesium the leaves will turn yellow.

Magnesium is an important nutrient and the effects will be felt in the entire plant. With a magnesium deficiency, you will also see some changes in the root or stem of the plant.

The reason this happens is that magnesium is a mobile mineral.

Is there any way to avoid magnesium deficiency in cannabis?

There are some ways to avoid magnesium deficiency in cannabis. Growing the plant in a controlled environment can help you use soil with the right PH so that magnesium can be absorbed properly in the soil.

Most of the time deficiency occurs when the plant is grown outside and the soil acidity or alkalinity is not favorable.

Another way to avoid deficiency is to use the right type of water for irrigation. Water processed through reverse osmosis is not the best for plant growth.

It does not contain any important nutrients and this can lead to a deficiency when irrigating the plant.

Using good quality products can also help avoid deficiency. If you are going to use fertilizer to boost your level, then you need to use the best quality fertilizer.

Avoid using a fertilizer that does not contain excess salt. Salt can be a big hindrance to magnesium absorption.

Always make sure that the magnesium is absorbed. In some instances, you may have magnesium in the soil or water but it is not available for poor PH or any other reason. Making sure that your magnesium is absorbed can help to avoid deficiencies.



About David Rhodes

David has been working in the cannabis industry for the past 17 years with experience working overseas in Amsterdam as a budtender for 5 years! His goal is to help you with your cannabis grow! Learn More About David!

David Rhodes