Recover from Magnesium Deficiency with your Marijuana Plants!

If you have a magnesium deficiency with your marijuana plants, you may not know for about a month.

As a silent killer it creeps up on a plant.

You may start to notice one day that your plants are looking sick, have drooping leaves, or curling with the leaf.


Providing the proper amount of magnesium is vital for plant growth and overall health.

It works best when combined with calcium, so your cannabis plants can get the right amount of vital minerals.

This combo is a must if you're growing hydroponically and even in soil.

If you are not sure if your plants are low in magnesium.

Let's first check out the signs.

Signs of Magnesium Deficiency

The deficiency can occur for 4-6 weeks before any symptoms appear.

Here is a list of the common signs:

  • Yellowing outside the veins of the marijuana leaf.
  • Brown spots appear on older leaves.
  • Leaves have a pale green color.
  • Old leaves curl, dry and start to fall off.
  • Look sick overall
  • Drooping appearance.
  • Tips of leaves may appear slightly burned.
  • Marijuana leaves curling down.

Click on image to enlarge.

magnesium deficiency marijuana diagram


Lets quickly take a look at what magnesium is and,

Why is magnesium important to marijuana?

magnesium symbol

Magnesium plays a significant role in the health of your marijuana plants.

It is a secondary nutrient to plants, which is responsible for the production of chlorophyll.

Without chlorophyll there is no photosynthesis. In turn no plant growth.

Magnesium aids synthesis of sugars in plants and protein for essential amino acids.

It also aids in the uptake of phosphorus in marijuana plants and helps to protect against drought conditions.

Magnesium works together with calcium to provide the perfect balance of essential minerals.

The lower leaves will start to show issues because magnesium is a mobile nutrient.

Check those leaves!


Yellowing outside the veins. A Sure Sign!


Causes of Magnesium Deficiency

  • Not using enough magnesium when growing or any at all.
  • Low PH soil (check your soil ph values )
  • When growing in hydroponic and coco, magnesium is essential. It’s suggested to provide calcium and magnesium to your marijuana plants.

You can also run into Magnesium Lockout.

Magnesium Lockout happens when the PH is below a certain level causing the medium to become acidic for the roots which stop's the uptake of magnesium by your plants.

Here are some PH values to watch for if they are below these values:

When growing in soil: PH levels of 4.0-5.5

Hydro and Soil Less Mediums: PH levels of 4.0-4.5    

magnesium deficiency marijuana leaf

Older leaf with browning occurring.

How to Fix Magnesium Deficiency

The best ways to fix magnesium deficiency with marijuana is:

Flush your plants first to remove old nutrients and old salt build up!

Correct the PH level in water/ nutrients.

The optimal ranges should be in the following markers:

Soil, 6.0 - 6.5 pH range. Hydro or coco coir, 5.5 - 6.5 pH range

Start supplementing with Cal Mag

Epsom salts can provide extra magnesium when needed, just add one teaspoon per gallon or 4 liters of water or with your nutrient feeding.

Dolomite lime, can be used but it must be added to the soil either on top of the soil or mixed in the soil.It’s usually easier to just use a Cal-Mag supplement.

Magnesium sulfate is like Epsom salts but with added sulfur.

Garden lime can adjust your soil's ph levels, and a little goes a long way!

Worm castings are an excellent organic choice are recommended to be mixed with soil for full benefits.



Magnesium for Cannabis:

Here are some magnesium only nutrients for your marijuana plants.

Dyna Gro Mag Pro is a nutritional supplement that helps boost magnesium and sulfur levels.  

It comes in a ratio of 2 percent  magnesium and 1.5  percent sulfur, one issue is it has a high phosphorus values that are: 2-15-4 so be careful when adding to adding to additional nutrients.

Cal Mag for Marijuana Plants:

Here are some of the popular Cal Mag for your marijuana plants.

Cal Mag Plus by Botanicare is an excellent calcium and magnesium supplement for your marijuana plants.

It comes with and the addition of iron, which is beneficial for plants.This is a favorite choice among growers.

The values are 2-0-0, which will bump your nitrogen levels in your feeding regime.

It has 2 percent nitrogen, 3.2 percent calcium, 1.2 percent magnesium, and .1 percent iron.

Cal-Mag Plus can be used in all types of growing: hydroponic or soil.

Hydro Organics Earth Juice Elements Cal-n-Mag can be used in soil or coco coir and is recommended for hand feeding systems only.

It can help bring your plants back from a deficiency in either calcium or magnesium.

Cal-n-Mag provides vigorous vegetative growth.

It contains 2 percent nitrogen and 3 percent calcium and 1 percent magnesium.

Advanced Nutrients Sensi Cal-Mag Xtra Plant Nutrient comes with the right ratio of calcium to magnesium.

It also has an addition of iron on top of the amino acids vital for plants growth.

Sensi Cal Mag has a high nitrogen level so watch out for that when adding it to your feeding schedule.

This is to be used with non-advanced nutrient products as they regular product line has addition cal mag in its grow nutrients. The ratio is 4-0-0.

After adding a supplemental Cal Mag to your plants they should start to recover within a couple of weeks if not sooner.

It all depends on how bad your marijuana plants were lacking magnesium and possibly calcium.

magnesium deficiency with marijuana

Signs of Excessive Magnesium

There may be a time that you are providing too much magnesium to your plant due to label recommendations.

Or it could be that your plants don't need as much magnesium as other pants do.

Not all cannabis plants require the same amount of nutrients.

It can be hard to have excessive levels, but it does arise.

Here are the following signs of too much magnesium.

  • Stunted growth
  • Dark green leaves.
  • Symptoms appears as an overall salt toxicity.

How to fix excess amounts of magnesium

The best ways to fix excessive amounts of magnesium in your cannabis plants is to try the following to repair the damage.

Flush your plants with water for a couple of feedings to try and clean the root structure.

Stop giving your plants magnesium for at least one feeding.

Start to slowly add small of amount of magnesium until your plants appears to have recovered.


When you encounter a magnesium deficiency with your marijuana plants sometimes it can be too late.

But, you should be able to recover within a couple of weeks by usually flushing your plants and adding a Cal Mag nutrient to your regular feeding schedule.

Cannabis plants love magnesium.

Often, they can take quite a bit, but as stated earlier some strains require more than others.

I hope you recover fast so you can enjoy the flowers of your labor.

Grow on my friends

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