Magnesium Deficiency In Marijuana Plants

The purpose of magnesium is to encourage strong, healthy veins and stimulus on the creation of marijuana leaves. It also plays a role in producing chlorophyll and breaking down enzymes.

Magnesium deficiency can happen in any plant medium and hydroponic system. But this rarely occurs when growing marijuana outdoors.

When signs of deficiency occur if must be dealt with quickly or else it will become a major problem causing the plant to quickly lose many of its lower leaves. Magnesium is a nutrient that can move around, so the plant has the ability to move it from the old leaves to new ones.

Your plant will take magnesium from the older leaves and move it to the new leaves. This explains why magnesium deficiency has a tendency to show up towards the bottom of the plant and on the older leaves.

Signs of a magnesium deficiency

Magnesium deficiency marijuana plant

Symptoms begin in the lower leaves when they start to turn yellow and show chlorosis. The leaves begin turning inward and will soon die. The outlining of the leaves will feel dry and brittle. The deficiency will move up to the middle and upper half of the leaf, and the growing shoots will start going from pale green to white. All of the petioles and stems will also become purple in color.

Sometimes you may notice light brown spotting on the edges if the issue continues to worsen, even though it is possible this could be a little bit of another deficiency that comes along with magnesium deficiency.

You can easily avoid and solve magnesium deficiencies once you are aware of how to handle it. We will go into more detail about this below. Not sure if your plants have a magnesium deficiency? Read the article Nutrient deficiencies in marijuana plants for a list with pictures of all deficiencies.

Using the correct nutrients and plant protector will get you a long way and your plants will have less chance of getting sick, in addition of being less vulnerable for pests and diseases. I have created multiple grow sets which features all you need in order to grow healthy plants from seed to harvest!

buy all-in-one marijuana grow set

Buy your grow set

How to fix a magnesium deficiency in weed plants

Late stage magnesium deficiency in marijuana plant

There are several ways to resolve magnesium deficiency, but one of the better options is a product called Marijuana Booster.  This is one is very popular amongst marijuana growers because it is great for enhancing the quality of yields and provides a good balance of nutrients.

More options are:

  • Dolomite lime
  • Magnesium sulfate
  • Garden lime
  • Worm castings
  • Epsom salts

Since both Epsom salt and Magnesium sulfate (wiki) are water soluble, they work the best. For hydroponics systems, Epsom salts are by far the simplest solution. For every gallon of water in your tank add a teaspoon of Epsom salts. Give it a quarter of the initial dosage for every consecutive treatment. If you like, you can even add Calcium-Magnesium (available at this link for only $20)

Magnesium and pH levels

Magnesium ph levels weed

If the pH of your plants roots get too low, the marijuana plant could display signs of magnesium deficiency, even more so in hydro (check these hydro ph levels). This occurs as a result of the pH of the roots not being at the right ratio, which causes the plant to not properly receive magnesium from the roots.

Usually with this deficiency, the magnesium is there, but the roots are not able to receive the magnesium efficiently because of the wrong pH. This is why it is necessary to keep the right pH so as to prevent magnesium deficiency.

Download my free marijuana grow guide at this link for more growing tips

Providing additional magnesium to a system that has a pH lock-out will most likely not help since the plant can’t take in any magnesium until the pH is made right. If your plant has plenty of magnesium, giving it more could result in the development of other deficiencies by shutting out other nutrients the plant needs.

If you’re growing marijuana in soil, magnesium is better received by the roots in the 6.0 – 7.0 pH rate. If your’re growing marijuana in hydro, magnesium is better received by the roots in the 6.0 – 6.5 pH rate.

Try Flushing

If suspicion sets in and you begin thinking you plant has a magnesium deficiency, flush the system with pure, pH’d water that has a normal dose of marijuana-friendly nutrients in it which should include magnesium. This serves to get rid of all nutrient salts that are may have damaged the plants ability to absorb magnesium and help replenish the pH to the right ratio.

Read the article How to rinse a hydro system for more information about flusing

Flushing might work with a lot of deficiencies, since you basically push the ‘reset’ button. However, it is always best to not have any issues in the first place! By using my Bergman’s Plant Food you will ensure a great grow. I have created this package so all nutrients are perfectly balanced specifically for growing marijuana plants!

buy marijuana nutrient set

All-in-one nutrient package

  • All the nutrients from seedling to harvest
  • Enough nutrients for at least 5 plants
  • Specifically balanced for marijuana plants
  • Suitable for soil, hydroponic and other growing mediums

List of marijuana plant symptoms

Leaf Color: 
– Edges Look Brown or Burnt
– Pale Color Leaves
– Lower and Older Leaves Turn Yellow
– Yellowing Between Veins
– Veins of Leaves Stay Green
– Brown or Dark Spots
– Speckled / Patchy Pattern

Leaf Symptoms: 
– Lower Leaves and Older Leaves Damaged
– Leaf Tips Look Burnt
– Leaf Tips Die
– Yellowing Between Veins
– Veins of Leaves Stay Green
– Spots
– Speckled / Patchy Pattern
– Old Leaves Dropping Off
– Twisted Growth
– Leaves Curl Under
– Leaves Curl Upwards
– Withering / Drooping

Plant Symptoms: 
– Old Leaves Dropping Off
– Twisted Growth
– Leaves Curl Under
– Leaves Curl Upwards
– Plant Withering / Sagging

Prevent deficiencies in your plants

Prevent magnesium deficiency weed

If you properly resolve the issue, the yellowing and discoloration of the leaves should cease almost instantly. Some damaged leaves could bounce back to a certain extent, but what matters the most is that you ensure the issue is not still spreading to the other leaves on the plant.

We suggest not getting rid of the discolored leaves until you are certain the issue is totally resolved and is not spreading to the newer leaves. It is better if any continued discoloration occurs on the leaves that were already damaged.

All in all, pay close attention to the growth of your plant and if you suspect any issues use the list of symptoms to determine if there is a deficiency. Once you have followed the proper steps to restore balance, remember that it may take a few days before the deficiency is completely cleared up.

Thanks for reading. Please leave comments or questions below and don’t forget to download my free grow bible


Avatar for Robert Bergman

Robert Bergman


Robert Bergman is an Amsterdam-based marijuana grow expert who has years of experience from small grows to massive operations ... See profile

10 comments on “Magnesium Deficiency In Marijuana Plants”

  1. I was advised to get crushed mites on my young plants, to mix 40% alcohal 60% water & spray leafs. Did rid of the mites, but a week later, the leafs turned almost white, very light yellow green now. Plant is still growing in veg state but not sure how to trouble shoot. looks like magn. issue but no one has been able to advise.

    • Mike,

      my advice is to join, and post some pictures.

      We cannot tell if you have a Mg deficiency without seeing the plant; Therefore, I cannot give you informed advice. Join the forum and we will give you honest and valuable opinions on what to do next.

      When you get to ILGM; Look for a support ticket, which is pinned at the top of the beginners forum

  2. SpaceCowboy207,

    The way you tell if your methods atr working is to monitor the new growth. That shows you if the plant is growing healthy.

    Damaged leaves can be removed when they are almost completely discolored, and maybe a little sooner. Prune lightly when you do in order to not stress the plant any further.

    I suggest that you join our Support forum and fill out a “Support Ticket” in a new topic. Let me know if you have any issues. You may not be allowed to start a topic until you have made a few posts, and spent a total of 20 minutes on the forum. Pretty easy to accomplish if you just peruse around and make polite posts in appropriate topics. Later, lw

  3. hey thanks for the great article!! this is he most detailed site for info i’ve found so far, full of excellent information. i am pretty sure i have a cal/mag deficiency, but it may have led to nut. lockout for all i know. it’s been roughly 10days since i flushed the plants until the pH levels where the same going into the soil as they were coming out. i then gave them a 1tsp/gal of cal/mag the next day and continued the regular feeding schedule. no improvement on 1/2 the plants ( all indica stains). how long till i can tell when the issue has been resolved? should i remove the discolored leafs sooner or later? repeat the process i mentioned again if not resolved? thanks ahead for any info.

  4. […] The easiest and most common way to fix a magnesium deficiency is the application of Epsom salts. Be careful, though, you want to make sure you’ve diagnosed the deficiency correctly before trying to fix it. If you apply too many unneeded nutrients, you could be causing a whole new problem instead of fixing the real issue. Read more about magnesium deficiencies in marijuana plants […]

  5. We are a worm casting business and have been wanting to test a mixture of castings with magnesium sulphate or dolomite for distribution as an additive in the same mixture/bag. Any advice?

  6. I’m a first-time grower and my plants have a calcium magnesium deficiency.. I started feeding the plants Cal mag a couple days ago my question is how long will it take for them to fully recover from this?? Will the damaged leaves repair themselves or should I just remove any unhealthy looking leaves?? Thanks