Magnesium Deficiency

Magnesium Deficiency in Cannabis Plants

If you’re into gardening as a hobby, you’ve probably wondered why your plants sometimes fail to thrive. Such questions are often followed by a certain degree of panic because there’s a chance of complete crop loss. Cannabis is a vital crop that provides much-needed relaxation or medication, so it’s doubly important that these plants grow to their full potential.

Of all the challenges cannabis growers face, magnesium deficiency is one of the most problematic. It doesn’t discriminate and it affects all strains and can strike at any time. Low magnesium levels can lead to crop failure if left untreated. With treatment and preventive measures, it’s possible to cure a magnesium deficiency and keep it from reoccurring.

How can growers tell the difference between a lack of magnesium or one of the other problems that may occur in the garden? We’re here to help. In this guide, you’ll learn how to assess, treat, and minimize magnesium deficiencies in cannabis plants. We’ll answer some vital questions such as:

  • How does magnesium help cannabis plants?
  • Is magnesium absorption affected by pH levels?
  • How long does it take for treatments to work?

That’s a lot of ground to cover, and we understand that the success of your crop is at stake so let’s get started!

The Importance of Magnesium

Magnesium or Mg is the periodic table’s twelfth element. It was first found in 1618, but it was not formally recognized as an element for another 137 years. In the early 1800s, magnesium was first isolated in its pure form. Since that time, we have found that magnesium is one of the building blocks of life, but neither plants nor animals make their own. Therefore, we must supplement our plants with this vital nutrient.

All of Earth’s plants absorb the sun’s light with chlorophyll. Through the process of photosynthesis, light is turned into nourishment for plants. Magnesium is a crucial component in chlorophyll molecules, and photosynthesis can’t happen without it.


Symptoms of a Magnesium Deficiency

Like most other plants, cannabis plants give warning signs when things go wrong. The following symptoms are important to look out for to determine a magnesium deficient marijuana plant:

  • Burnt leaf edges and tips
  • Dead leaf tips
  • Pale-looking leaves
  • Damaged older and lower leaves
  • Yellowish areas between leaf veins
  • Dropping older leaves
  • A patchy, spotty, or speckled pattern on leaves
  • Twisted growth patterns in leaves or entire plants
  • Leaf curling, drooping, and withering
  • Sagging of entire plants

These symptoms typically start in the lower leaves and, with time, work upwards to the rest of the plant. If a magnesium deficiency is left unaddressed, a plant’s growing shoots will turn white and its stems and petioles will acquire a purplish tinge.


Developments of a Magnesium Deficiency

First Months: Plants exhibit no outward signs. They may look dark green and healthy.

The first signs: May appear at around the sixth week. Small, rusty necrotic patches may appear on leaves under blooming buds. However, fruit development progresses normally.

Additional signs: Necrotic patches spread across more leaves, and chlorosis may cause the leaves to look yellow.

As symptoms spread: The plants may look saggy or wilted.

Serious signs of spread: When plants have a serious magnesium deficiency, leaf production may slow down or even stop.

Preventing a Magnesium Deficiency

The easiest and most effective way to minimize issues is to give your plants the love and care they deserve. Regularly inspect the plant’s stems, stalks, and leaves. If there are problems, do your homework and take immediate action.

Another simple way to minimize the risks associated with magnesium deficiency is to begin with a quality growth medium and top-quality cannabis seeds. Many vendors sell soil that’s specially formulated for marijuana plants, or if you are fortunate enough to live in an area where cultivation is legal, it may be possible to find it at a garden center.

To improve the chances of cultivation success, start at the source. The budtenders at local dispensaries may be able to tell you where to find quality seeds or soil. However, it’s easier and safer to buy your seeds from a reputable and reliable seed bank such as

Additional Factors that Can Contribute to a Magnesium Deficiency

Any cannabis plant can suffer from a deficiency if the condition of the growth medium isn’t carefully monitored. Growing marijuana plants outdoors will resolve the problem to an extent, but even natural soil sometimes has low magnesium levels.

Cannabis plants cultivated in grow rooms are more likely to suffer from magnesium deficiency because the soil might not have enough magnesium required to support growing plants. Later in this guide, we will show you how to resolve this issue. Before we do that, though, it’s important to consider that signs of deficiency may not be due to low levels of magnesium in the soil; the problem may be due to the soil’s pH.


How the Soil’s pH Level can Affect the Absorption of Magnesium

The soil’s pH can play a big role in how your marijuana plants are able to absorb magnesium. The soil’s pH is a measurement of its amount of base or acid. Cannabis plants prefer a mildly acidic growth medium (a pH of 6-7), and anything below or above that range will lead to issues.

If the soil’s pH is too high or too low, the plant’s roots will not absorb nutrients even if they’re plentiful. Your plants may have all the magnesium they need, but when the soil’s pH is out of line, the element cannot do what it’s designed to do. Thankfully, the fix for this issue is rather simple.

  • Buy a pH decreaser or increaser from a nearby garden center.
  • Carefully follow the directions on the container.
  • Celebrate whent your marijuana plants no longer exhibit the symptoms of a magnesium deficiency.

Even if the soil’s pH is ideal, plants can suffer from a lack of magnesium. Read on to learn how to ensure your cannabis plants receive all the nutrients they need.

How Other Nutrients Play a Role

Magnesium absorption is partly determined by the presence of certain other elements. Generally, nutrient levels are kept in balance with a 4:2:1 ratio of potassium to calcium and magnesium. If there’s too much of any nutrient in a solution, the plants aren’t as able to absorb enough of the other two nutrients. These antagonistic situations are quite common in tomato crops, where high doses of calcium are used to prevent blossom rot. In geraniums, quantities of flowable lime or dolomitic limestone are used to balance the soil’s pH. Elevated calcium levels limit magnesium uptake in plants, and your cannabis crop is no exception.


Resolving Magnesium Deficiencies in Cannabis Crops

To make up for a magnesium shortfall in cannabis plants, you’ll have to add supplements to the soil. Visit your nearest lawn and garden center and choose one of these options:

Then, thoroughly read the package instructions. We suggest starting with Epsom salt because it’s inexpensive, widely available, easy to use, and very water soluble. Follow these directions to help your soil, resolve its magnesium deficiency, and get your cannabis crop back to good health.

  • Add a teaspoon of Epsom salt to a gallon of clean water and stir.
  • Hydrate your crop as usual.
  • When that gallon of water has been used, add ¾ teaspoon of Epsom salt to one gallon of water, hydrating your crop normally.
  • Gradually reduce the amount of salt by ¼ teaspoon per gallon of clean water.

During the process, proper soil pH monitoring is crucial. The soil’s pH and nutrient level are the most common causes of magnesium deficiency. By observing these two factors, you’ll ensure the success of the crop.

When you’ve gotten to the root of the issue (pun certainly intended), most of the plant’s leaves will quickly regain their lush green color. Though it’s difficult to observe the recovery process, in most cases, a bedtime watering will bring substantial improvement by morning.

Though some of the leaves might not recover, that’s not a cause for concern. The most important thing is to keep the withering and discoloration from spreading to the rest of the plant. If only a few bottom leaves are wilting but the plant otherwise looks healthy, you’re in relatively good shape.

Bottom Line

Nutrient deficiencies are a common challenge among cannabis growers, but with the abundance of information and beneficial supplements, they’re easy to overcome. When facing a magnesium deficiency, take notes on what works and what doesn’t. With the experience gained, your next crop will be much more successful.

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