How Can Epsom Salt Benefit Your Cannabis Plants?

No matter your experience with growing cannabis, there's one simple principle that never changes—healthy plants give heavy yields. Satisfy all of your plants’ needs, and the reward is dank, resin-laden buds bursting with cannabinoids and terpenes. But, with so many factors to consider, how can you make sure plants grow lush, green and full of vigour? The answer is Epsom salts, an organic supplement used by humans and cannabis plants alike.

What is Epsom Salt?

Epsom salt is a natural supplement that was first discovered in Epsom, a small town in Surrey, England. Although, it’s fair to say the townsfolk weren’t entirely sure of what they’d stumbled across at first.

After noticing cattle wouldn't drink from a pool of water, a local cowherd tried it for himself, only to discover a bitter taste. He also noticed a strange salt upon evaporation. Remarkably, the supposed salt was a rather potent laxative. This was good news for society, as Epsom Salts became the go-to constipation treatment for the next 350 years, but we imagine the unknowing cowherd didn't have a good time.

While it may have been beloved for its bowel-cleansing properties, it now finds frequent use in gardens around the world. In fact, for cannabis growers, and gardeners in general, Epsom salts are a golden ticket to healthy plants and bountiful yields. Why? Because Epsom “salt” isn’t salt at all; it’s actually magnesium sulphate! If that sounds familiar, it’s because that compound consists of magnesium and sulphur, two essential macronutrients that plants, including cannabis, thrive on.

When to Use Epsom Salt

Although it's tempting to dose all your cannabis plants with Epsom salts, in truth, it's not really needed if your plants are already healthy. However, if you're growing outdoors in soil with low magnesium or your cannabis plants start to show a magnesium deficiency (yellowing fan leaves), then it's time to bust out the Epsom salts.

Magnesium, Sulphur and Cannabis Plants

As we've highlighted, the invigorating quality of Epsom salts is rooted in magnesium and sulphur. Both work behind the scenes to bolster your cannabis plants in many ways.

• Why cannabis plants need magnesium

  Magnesium is an essential macronutrient because it facilities the uptake of more abundant nutrients (nitrogen, phosphorus and potassium). Better absorption of nutrients, in turn, comes with a whole host of benefits, including sturdier growth, a more impressive size, and larger yields on top of that. For the most part, you shouldn't need to supplement magnesium if you have a robust soil mix, but you'll quickly notice if plants are lacking. Magnesium deficiency exhibits itself as yellowing leaves, with green veins still visible. It's also common for the lower leaves to show these signs first, before spreading to the rest of the plant if you don't deal with the deficiency.

• Why cannabis plants need sulphur

  Sulphur acts similarly to magnesium, improving the uptake of other nutrients. However, it also plays a crucial role in your plant's immune system and the production of enzymes, amino acids and vitamins. And, as a final feather in the cap, sulphur is essential for helping cannabis plants manage water in and out of the soil. The benefits of sulphur are especially important if you plant needs a long time to grow, as a robust immune system is needed to deal with the environmental stress.

Benefits of Epsom Salt

There are dozens of benefits to using Epsom salt on cannabis plants. Below you'll find a breakdown of the most significant advantages.

1. Eco-friendly and cheap

The cost sits at the back of every grower's mind, and there’s a question of whether the investment is worth the returns. Thankfully, with Epsom salts, the initial price is incredibly cheap, and the product is readily available in garden centres across the world. Just make sure to avoid Epsom salts intended for human use, as these can contain extra additives or chemicals your cannabis plants won't like. Epsom salts are also fantastic for the environment, so you don't need to worry about contaminating soil once you do get your hands on some.

2. Won't build up in soil

It's common for minerals and supplements to build up in soil, especially if you're enthusiastic with dosing. However, Epsom salts differ, dissolving easily in soil. They won't build up and block roots from getting the nutrients they need. It goes the same way in hydroponic systems, too, so you can use Epsom salts without worrying about overdoing it and causing more problems than you solve.

3. Improves nutrient uptake

We've already highlighted this particular benefit, but it's worth clarifying. Both magnesium and sulphur improve the uptake of nutrients such as nitrogen, phosphorus, and potassium. Together these elements form the building blocks of cannabis growing, and a balanced ratio of the aforementioned nutrients will help your plants reach their full potential.

4. Encourages the creation of chlorophyll

Without chlorophyll, plants wouldn't be able to absorb sunlight. And, without sunlight, there would be no photosynthesis. That means no growth, no leaves, no buds—nothing. In steps, Epsom salts—or—more specifically, magnesium, help with this fundamental process. This essential mineral facilitates the creation of chlorophyll, strengthening the process of photosynthesis, and the growth that happens as a result.

5. Maintains your plant's structure and health

All growers want their cannabis plants to be healthy and well-developed. Fortunately, Epsom salts can help on this front too. By supporting the uptake of nutrients, encouraging photosynthesis, strengthening cell walls, and encouraging the production of essential amino acids, Epsom salts work alongside your plant's natural processes, bolstering their health from the ground up.

6. Plays a crucial role in seed production and germination

A quality of Epsom salt we haven't touched on is its ability to remove sulfites from soil and hydroponic systems. A small amount of sulphites is ok, but too much can damage the roots. This, in turn, inhibits germination, stunts growth and causes nutrient deficiencies. Epsom salts, to help you avoid this, gently remove sulfites. This removal also leads to potentially higher rates of germination, while the extra magnesium supports seed formation if pollination and breeding is your goal.

7. Pivotal for long-life plants

We alluded to this already, but Epsom salts can help significantly with plants kept in the vegetative phase for extended periods. Typically, cannabis plants flower once a year, but some want to promote longevity in mother plants earmarked for cloning or breeding. If you’re in that situation, Epsom salts are a valuable ally. They work to remove any nutrient build-up, and reduce the environmental stress incurred as well. You can essentially reset imbalances mother plants may have picked up throughout their extended veg period.

8. Can revive mothers and root-bound plants

If your mother plant has taken a turn for the worse, or plants appear rootbound, a dose of Epsom salts could alleviate both problems in one fell swoop. Both mother plants and root-bound cannabis suffer from a build-up in sulphites. A light dose of Epsom salt cleans root cells, kicking them out of a dormant phase, and getting them back into action.

How to Use Epsom Salts

Perhaps the most significant benefit of Epsom salt is how versatile and straightforward it is to use. Even a small amount can be advantageous for cannabis plants in both soil and hydroponic growing mediums.

In soil

For germination and seedlings, we recommend using one teaspoon per 5 litres of water. However, don't apply the solution directly. Instead, diffuse it using a spray bottle, and give plants a light misting once every 2-3 days. If you’re spraying plants, try to do it when the lights are off, or towards the end of your plants light schedule to prevent light burn.

Misting Bottle (Zamnesia)

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For mature cannabis plants, you can water plants directly using the same ratios outlined above. Remember, Epsom salts prove most effective in soil already lacking magnesium. If your soil has a high pH (7 or above), consider full watering with Epsom salts to replenish the nutrient balance.

In hydro

For hydro setups, following the same dosing recommendation as soil, but only if you're applying Epsom salts via a foliar spray. And, just like soil, avoid spraying your hydro cannabis plants when the lights are on, as this can cause light burn.

If you want to mix Epsom salts directly with your hydroponic system, add up to 2 tablespoons per 5 litres of water. For an even consistency, it also helps to dissolve the Epsom salts in lukewarm water first.

Can you Use Too Much Epsom Salt?

Too much magnesium and sulphur can still damage your plants, blocking the uptake of other essential nutrients. However, that being said, it's incredibly challenging to overdo Epsom salts. As long as you stick to the recommended dosage guidelines, you shouldn't have any problems. But, of course, every setup and every cannabis plant is unique, so use your judgment. In most cases, we recommend starting with a low dose of Epsom salts and increasing as needed. Overall, with a balanced approach, Epsom salts are a simple and highly valuable addition to any growers arsenal.

Luke Sholl

Luke Sholl has been writing about cannabis, the wellness potential of cannabinoids, and the positive influence of nature for over a decade. Working with several cannabinoid-centric publications, he publishes a variety of digital content, supported by strong technical knowledge and thorough research.

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