Medically Reviewed by
Jason Crawford

Article Last Updated on December 25, 2022

For every cannabis grower, the health of their cannabis plants is a top priority. Getting quality yields of weed brimming with fragrant terpenes and powerful cannabinoids like CBD and THC is a rewarding feeling only successful growers know. Once you’ve mastered it and found your perfect system for keeping those crops in the best shape possible, it becomes a routine, but what about growers who have just entered the business?

There are many ways of keeping your cannabis garden thriving and producing the best-tasting weed, and one of them is using Epsom salt. If you’re not too familiar with this supplement, keep reading to find out how Epsom salt can be used to improve the condition of your cannabis and bring out the best in it.

What Is Epsom Salt?

Epsom salt is another term for magnesium sulfate, a naturally occurring mineral discovered in the spring waters of Epsom, a town in Surrey, England. Way back when, the farmers in Epsom discovered that the cattle wouldn’t drink from the water, and upon tasting it found out that the water was bitter and there was a leftover of salts upon evaporation. Soon, the healing properties of Epsom salt were established and it was used to treat all kinds of ailments, from muscle aches to treating colds.

Nowadays, Epsom salt is also used as a gardening supplement because of its magnesium and sulfate content, which is highly necessary for maintaining the plants’ health. When it comes to growing cannabis, Epsom salt is an excellent choice for feeding the crops which ensures you’ll get nice and fragrant buds.

You can find Epsom salt in any gardening store or even health food stores, just make sure to avoid cosmetic Epsom salt, as it tends to have a lot of additives, like dyes, perfumes, and essential oils which can damage your crops.

Why Do Cannabis Plants Need Magnesium?

Marijuana needs magnesium because it aids the uptake of phosphorous, nitrogen, and sulfur from the soil, which are essential micronutrients necessary for the plant’s survival. Magnesium is also important for the creation of chlorophyll, which plays a vital role in photosynthesis. Without it, your cannabis plants won’t be able to absorb energy from the sun to convert it into food for survival. Magnesium also aids seed production and it strengthens the cell walls.

Why Do Cannabis Plants Need Sulfur?

Sulfur has a similar role to magnesium in that it improves the uptake of other essential nutrients. In addition to this, it boosts the production of enzymes, amino acids, and vitamins, aiding your marijuana’s immune system and helping it to protect itself from infestations. Sulfur is also needed for the longevity of the crops and to protect them from environmental stress.

How to Recognize Deficiencies in Your Plants

Keeping a close eye on your crops is vital in keeping them as healthy and bountiful as possible. Noticing deficiencies is nothing to worry about as long as you do something about it before it significantly affects the plants.

A magnesium deficiency manifests as yellowing between the veins of the plant, usually at the bottom leaves. The plant may look kind of droopy and dull, instead of lively. Sulfur deficiency manifests as similar yellowing of the leaves, but some of the buds may also come loose or look like they’re about to fall off.

In any case, an intervention will definitely be needed if you want to restore the health of your cannabis plants.

How to Use Epsom Salt

Using Epsom salt is pretty straightforward – there are no complicated set-ups, different tools, or schedules you need to follow. It’s pretty simple and easy for any growing method you use. The only thing you need to pay attention to is consistency and monitoring your plants’ response.

  • For soil, it’s best to use one tablespoon per about four liters of warm water, or a little less than a gallon of water, and let it cool completely. Then, instead of watering the plants directly, pour the mixture into a spray bottle and use it as a foliar spray. Spray the leaves of the plants, especially the underside at the beginning of each cycle, but not during the first week of flowering. You should also avoid spraying them with the lights on as the effect will be much stronger. If your soil has a pH of 7 or above (which is high), you can water them to replenish the nutrients.
  • For hydroponics, it’s more or less the same as with soil, but if you want to add Epsom salt directly into your system, you should put two tablespoons instead of one. However, you should continue to be diligent with following the pH balance of your hydroponic system as it can easily change, and don’t forget to monitor the nutrient levels.

The Benefits of Epsom Salt

Besides being so multifaceted and useful in so many ways for humans and plants, Epsom salt has some added benefits that only contribute to its appeal.

  1. Sustainable – since Epsom salt is a natural ingredient, that makes it incredibly friendly to the environment compared to some other CalMag supplements;
  2. Cost-effective – it’s one of the cheapest garden products out there that’s easily available in any garden center, therefore, your investment will be worth it;
  3. Doesn’t cause build-up – minerals are known to cause build-ups in soil, making it harder for the roots of the plants to absorb the needed nutrients, but Epsom salt dissolves very easily, which is why it’s also suitable for hydroponics;
  4. Helps with nutrient uptake – Epsom salt aids marijuana plants in getting all the necessary nutrients from the soil in the most effective and natural way possible;
  5. Can revive mother plants and root-bound plants – these tend to be quite prone to a build-up of sulfites, so when you give them a little Epsom salt, it wakes them up by cleaning and refreshing the root cells, and gives them a kick.


Using Epsom salt isn’t hard science. The process itself is very simple and the plants love it. However, there may be a couple of things worth mentioning to avoid unnecessary issues.

Can You Use Too Much?

Technically, too much of anything is rarely a good thing, but somehow, Epsom salt is very forgiving when it comes to the amount you use. This means that even if you use a little too much sometimes, it won’t immediately affect your crops in a bad way. But, if you continuously overfeed them with Epsom salt thinking it’s for the better, it may do more harm than good over time.

If this happens, you’ll notice a yellowing in the center, slowly spreading to the outer corners of the leaves if it progresses. Should this happen, reduce the amount for a while and monitor the reaction of your plants. Otherwise, try to be moderate with using Epsom salt and your crops should be more than fine.

When Epsom Salt Doesn’t Work

Epsom salt may sound like a magical nutrient solution to all problems with cannabis nutrient deficiencies, but the truth is, plants need so much more nutrients than just magnesium and sulfate to fully thrive and give you bountiful yields. Sure, Epsom salt will help with a lot of issues, but plants also need calcium, and not to mention nitrogen, phosphorus, and potassium, the inseparable trio.

Therefore, if it happens that your plant doesn’t thrive despite the Epsom salt supplement, it probably means that you need to up the other nutrients as well. You’ll also want to consider the overall condition of the soil you’re growing your marijuana plants in and evaluate its nutrient level. The most important thing is the health of your crops, so make sure to examine your whole setup if you notice there are deficiencies despite your efforts.

Bottom Line

Epsom salt is the other name for magnesium sulfate, a naturally occurring compound that has many uses ranging from medical and cosmetic, to botanical. It’s a wonderful supplement for cannabis plants because it provides them with essential nutrients like magnesium and sulfate which play important roles for the plant’s health. It’s especially useful when the plants are sulfur or magnesium-deficient, but it can also be used preventatively as a boosting agent as it’s very forgiving when it comes to dosage.

A passionate advocate for the benefits of cannabis. Fraser Horton, who has a background in botany and a strong love of nature, has spent years researching how cannabis affects the body and mind. He established Leaf Nation in 2020, where he has devoted himself to educating people about the legalisation of marijuana and its safe and responsible use. Fraser is committed to highlighting cannabis’ potential for improving wellness and working to dispel the stigma associated with its use.


The information presented on this page is provided as a public service to aid in education and is derived from sources believed to be reliable. Readers are responsible for making their own assessment of the topics discussed here. In no event shall Leaf Nation be held reliable for any injury, loss or damage that could happen if using or abusing drugs.