Preventing Magnesium Deficiency in Cannabis Plants

Magnesium Deficiency
December 03, 2020

Magnesium is essential in all the stages of plant life. It is the core element of chlorophyll, which plays a crucial role in photosynthesis. With severe magnesium deficiency, cannabis plants will eventually die.

What does weed suffering from magnesium deficiency look like, and what should growers do to help it recover? With our expert and practical advice, this cannabis growing crisis can be avoided or overcome.

Identifying Magnesium Deficiency

Marijuana deficiencies can be broken down into the “Big Three” – nitrogen, potassium, and phosphorous – as they are the easiest to identify. However, there are rarer marijuana nutrient deficiencies that can cause significant growth problems or even plant death; one of them is a deficit in magnesium.

Once inflicted with magnesium deficiency, weed will struggle to grow and may even die eventually. There is tons of information to know, so keep reading to learn how to handle this concern like a pro.

Diagnosing magnesium deficiency cannabis

What and Why It Is Needed?

Humans, animals, and plants need magnesium, yet none of the three can produce it. Fortunately, Mother Nature created the mineral in abundance, making it the eighth-most copious element found on the crust of Earth. As a marijuana cultivator, understanding what the nutrient does and why a growing plant needs it are part of the job, so let’s get started.

Dissolving soil in water allows marijuana roots to absorb magnesium. Being a mobile nutrient, once taken in, the plant can move it from the older leaves to the new ones. In the case of magnesium deficiency, cannabis plants will pull the nutrient from older, less essential leaves at the bottom of the plant and move it to the younger leaves at the top of the plant. This natural survival mechanism tells you exactly how essential the mineral is.

Magnesium is the driving force behind photosynthesis in plants. It is the heart of chlorophyll, the green pigment found in plants, and it cannot form without the said nutrient. In the absence of chlorophyll, the plant cannot capture energy from the sun or artificial light source for the all-critical photosynthesis.

This means your cannabis cannot create its own food. This can be a problem during any stage of the growth cycle, magnesium deficiency during flowering will cause a massive reduction in bud production.

If this concern is not addressed and corrected early enough, the weed may wither and die. This element is also the reason why leaves have a green color. Do you now see the importance of magnesium in the life of your marijuana?

Signs of Magnesium Deficiency

As mentioned, your cannabis plant moves its supply of magnesium from older leaves to the new leaves during times of deficiency. The lack of the mineral and, therefore, chlorophyll will first manifest on the lower part as this is where the old leaves are. If not resolved, the middle foliage, then the upper portion, and, eventually, the colas and the leaves will also exhibit these symptoms:

  • Appear damaged
  • Start to yellow between the veins (an indication of chlorosis)
  • Develop spotty, speckled, or patchy patterns
  • Develop a twisted growth
  • Curling inward
  • Wither, droop, or fall off (especially the old ones)
  • Leaves and buds go from pale green to white

The tips of the leaves may also look brown or burnt, feel dry and brittle. Other signs include petioles and stems turning purplish or reddish. The plant itself may wither or sag.

How to Fix Magnesium Deficiency

Magnesium deficiency-related problems are easy to resolve. Like all plant health concerns, of course, prevention is best. However, if symptoms have already appeared, taking early action can reverse or stop the damage. Read on to learn how to handle this concern properly.

Check and Adjust pH Levels

If you suspect that your marijuana has a magnesium deficiency, you must check the pH value of the medium, water source, and nutrient solution. The pH scale measures their acidity or alkalinity, and it ranges from 1 to 14, with 7 being the neutral rate.

Cannabis plants thrive on a slightly acidic environment that is between 6.0 and 7.0. Hydroponic, meanwhile, systems can go as low as 5.5 to 6.0. It cannot absorb nutrients if the pH level of its root zone is above or below the ideal range, resulting in the deficiency of magnesium and other nutrients. In this case, the availability of the mineral is not the problem, but the condition that allows its uptake.

Each nutrient you add or remove from the environment affects the pH and, therefore, the general absorption of nutrients. Understanding this unique relationship will be of great help in cultivating healthy cannabis plants. You must measure the pH value regularly and adjust accordingly if it goes out of the ideal range.

  1. Check the current value using pH testing strips or a pH meter, which you can buy from a local gardening supply shop.
  2. If the result is not within the ideal range, use either a pH increaser or decreaser. You can also buy the products from the local garden center.
  3. Follow the packaging instructions of the product to be used.

Please do not add more magnesium to the medium, as it could cause a pH lock-out. This could make matters worse as it could shut out other nutrients, resulting in the development of other deficiencies.

Perform a Nutrient Flush

If the pH level is optimal, you must take an inventory of the nutrient diet of your marijuana plant. Check if you have been feeding it too much. If this is indeed the case, then you must perform a flush to free up your plants of the nutrients and start fresh.

Do this by running pure water through the medium of your cannabis plant. Use water that is within the ideal range – between 6.0 and 7.0 for soil and 5.5 to 6.0 for hydroponics. Excessively saturate the pot and repeat after 15 minutes. This should clear the nutrient blockage that formed in the medium but still check the purity of the water runoff using a TDS (total dissolved solids) meter. The result must be close to the TDS value of the pure water you used to flush the pot with. This ensures that most or all of the nutrients have been washed out, and the pH has been replenished to a suitable ratio.

Nurse Your Marijuana Plant Back to health

Once your plants can absorb proper amounts of magnesium again, the symptoms of deficiency will stop spreading to other leaves within a few days. The damaged leaves are unlikely to recover fully, so pay close attention to the most critical sign of success instead – the healthy growth of your plant.

First, we have to make sure that the issue is resolved entirely. Do not get rid of the affected leaves. In case the problem persists, the discoloration will continue on the leaves that were already damaged, sparing the newer leaves. If no further deterioration is observed after a couple of days, we can safely assume that the concern has been cleared.

At this point, you can remove the discolored leaves but only prune lightly. This is to avoid stressing the weed yet again. If they are not discolored, leave your fan leaves intact, so they can continue serving their crucial purpose. Do this even if there is a heatwave.

Recovering from magnesium deficiency cannabis

Continue monitoring the overall health of your cannabis. The new growth will display whether the plant is in optimal condition or otherwise. If you suspect an issue, refer to the list of symptoms in this article to determine if it may be a recurring deficiency in magnesium. Follow the same steps to create a root environment that encourages maximum nutrient absorption. Again, it may take a few days before the concern completely clears up.

If you would like to have better chances of not going through the same trouble, lower your risk by starting with high-quality seeds. Cannabis plants with strong genes have lesser chances of getting sick, especially when grown in a favorable setting. We recommend Homegrown Cannabis Co. seeds for marijuana strains with proven stabilized genetics at affordable prices.

Supplementing with Magnesium

Magnesium and calcium deficiencies often appear together. This is often referred to as Cal-Mag deficiency. For this reason, many marijuana cultivators use Calcium-Magnesium supplement, more popularly known as Cal-Mag, for their grow operation should such concern arise. The combo is well-suited for soil, hydroponic, and coco coir media. Other options include:

  • Dolomite lime
  • Epsom salts (hydrated Magnesium sulfate)
  • Garden lime
  • Worm castings

Because Epsom is water-soluble, it works best for feedings. It is especially popular with hydroponic growers. For every gallon or about 4 liters of water in the reservoir, add one teaspoon of Epsom salt and let it dissolve. Then, give it a quarter of the initial amount for every consecutive treatment. Cal-Mag deficiency during veg stage is quite common.

Resolving Magnesium Deficiency Fast

Magnesium, although only labeled a secondary nutrient, is a major element in the growth of marijuana plants. Inadequate amounts of this mineral may cause yellowing leaves, withering, or even plant death. Besides prevention, strict monitoring for the early signs of magnesium deficiency is crucial.

This ensures that the concern is addressed and resolved fast before it could inflict real damage on your weed and potential crop. When it comes to magnesium deficiency, cannabis plants can be rescued and healed quite easily before it becomes a lethal problem.