Does Epsom Salt Help Tomatoes to Grow? 3 Myths Busted!


Whether you are a new or experienced gardener, you may have heard that Epsom salt helps tomatoes to grow.  I was wondering if this is true or not, and if so, when to use Epsom salt.

So, does Epsom salt help tomatoes to grow?  No, Epsom salt does not help tomatoes to grow.  In fact, too much Epsom salt can actually cause excessive magnesium in your soil.  This can lead to a calcium deficiency in your tomatoes, leading to blossom end rot.  Epsom salt should only be used as a garden supplement if your soil has a magnesium or sulfur deficiency.

Of course, there are cases where Epsom salt can be helpful in your garden to correct short-term problems (such as a specific nutrient deficiency).  However, there are other alternatives that take a more long-term approach to the health of your garden soil.

Let’s take a closer look at Epsom salt, including:

  • What is Epsom salt?
  • when to use Epsom salt in your garden
  • how to use Epsom salt
  • myths about Epsom salt in gardening
  • alternatives to promoting soil health

What is Epsom Salt?

Epsom salt is magnesium sulfate, and it contains magnesium, sulfur, and oxygen atoms, along with water molecules.  It is well-known as a garden supplement, although it is overused in many cases.

magnesium sulfate
Epsom salt, or magnesium sulfate, can supplement magnesium and sulfur in your garden soil. However, it is not the cure-all that many believe it to be!

It is also known as an addition to a hot bath to help relieve sore muscles.  It can also be consumed in water to act as a laxative.

When to Use Epsom Salt in Your Garden

Since Epsom salt contains magnesium and sulfur, it is a good candidate for a soil supplement if your plants are suffering from magnesium or sulfur deficiency.  A magnesium deficiency in plants is far more common than sulfur deficiency.

Before you add Epsom salt to your garden, make sure that you really do have a magnesium deficiency in your soil, as opposed to a pH imbalance (more on this later).

Magnesium is important because it is the central atom in a chlorophyll molecule, as shown below.

chlorophyll molecule
Notice that chlorophyll has a central magnesium atom.

Chlorophyll gives plants their green color, and is essential for energy production through photosynthesis.  A lack of magnesium in a plant means a lack of chlorophyll, which leads to a lack of energy, slow growth, and possibly even death.

One sign of magnesium deficiency in a tomato plant is interveinal chlorosis, where the leaves turn yellow but the veins stay green.  The older leaves, which are lower on the tomato plant, will turn yellow first, and the higher leaves will follow suit later.

interveinal chlorosis
This leaf is displaying interveinal chlorosis: green veins, but yellow between the veins.

This is because magnesium is a mobile nutrient – the plant can move magnesium throughout its tissues easily, and so it will try to keep the newest leaves (the ones high up on the plant) healthy for as long as possible.

For more information, check out my article on magnesium deficiency in plants.

Remember: before we add Epsom salt, we need to find out whether the soil is deficient in magnesium or not.

How to Tell if Your Soil Has a Magnesium Deficiency

The best way to do this is to take a sample of your soil and send it to your local agricultural extension for a soil test.  They will be able to tell you the soil pH, along with the levels of various nutrients, including magnesium.

For more information, check out my article about soil tests and how to do them and my article on what a soil test tells you.

They will also be able to provide advice on how to treat a problem in your soil, such as a nutrient deficiency or pH imbalance.

A pH imbalance affects the availability of nutrients in your soil, which prevents plants from absorbing them. For more information, check out this article from research gate about pH and its effect on nutrient availability.

If your soil pH is too low (acidic), they may recommend adding lime (calcium carbonate) to your soil, which also supplements calcium.  Be careful with this, since excessive calcium can prevent a plant from absorbing magnesium!

calcium carbonate
Lime, or calcium carbonate, can be a helpful soil supplement, when used correctly.

A better alternative is to add dolomitic lime, which raises pH and also supplements magnesium (it contains both calcium carbonate and magnesium carbonate).

If your soil pH is too high (basic or alkaline), they may recommend adding sulfur to your soil. For more information, check out my article on lowering your soil pH.

How to Apply Epsom Salt in Your Garden

If a soil test determines that your tomato plants or your soil actually do have a magnesium deficiency, then there are a few ways to apply Epsom salt as a remedy.

Blend Epsom Salt Into Soil Before Planting

One option is to blend some Epsom salt into your soil at the start of the growing season.  To avoid using excessive amounts of Epsom salt, put a little (1 or 2 tablespoons) into the hole for each tomato plant before planting.

This will alleviate a magnesium deficiency in your soil so that your tomato seedlings can grow quickly.

Add Epsom Salt To Soil Around Tomato Plants Mid-Season

If your plants begin to display the signs of magnesium deficiency (see above), then it may be a good idea to supplement magnesium in the middle of the growing season.  One good way to do this is to work some Epsom salt into the soil around each tomato plant.

Remember that Epsom salt is extremely water-soluble, so leaving it on the surface of the soil around your plants may allow the rain to wash it away.  Make sure to work the Epsom salt into the soil to allow the tomato plant’s roots to absorb the nutrition it needs.

Foliar Feeding With Epsom Salt (Foliar Spray)

Another way to supplement magnesium to plants showing a deficiency is with foliar feeding, using an Epsom salt solution.  To make the solution, dissolve 2 tablespoons of Epsom salt in one gallon of water.

Then, put the solution in a spray bottle, and spray on the leaves of your tomato plant.  One word of caution: make sure to do this on a dry day, in the morning.

If you spray the leaves of the plants in the evening on a humid day, the leaves may stay wet for too long, which can increase the chance of plant diseases gaining a foothold in your garden.

Myths about Epsom Salt in Gardening

As mentioned before, the benefits of Epsom salt in gardening have been overstated in many cases.  It’s time to bust a few of the myths regarding Epsom salt.

Blossom End Rot

One huge myth about Epsom salt concerns blossom end rot.  Regardless of what you may have heard, Epsom salt cannot prevent or cure blossom end rot.

In fact, adding Epsom salt to your soil can actually cause blossom end rot.  You may be wondering how – let’s get into that.

Remember that blossom end rot is caused by a calcium deficiency in tomato plants.  The tomato ends up getting a brown or black spot on the bottom of the fruit (pictured below)

A few tomatoes with a bit of blossom end rot on the bottoms.

A calcium deficiency in your tomato plant is caused by one of these causes:

  • lack of water, or uneven watering
  • calcium deficiency in your soil
  • pH imbalance in your soil (pH too high or too low)
  • nutrient imbalance in your soil (too much of another nutrient that competes with calcium for uptake)

In the first case, the solution is to pay attention to your watering schedule, and to not over or under water your plants.  Adding Epsom salt will not help with this.  Adding organic material to your soil will help it to retain moisture, and adding worms can help to loosen the soil so that it drains better after a long rain or watering.

In the second case, adding Epsom salt to your soil will not do anything to solve the calcium deficiency in the soil.  The reason is that Epsom salt does not contain any calcium. For more information, check out my article on treating calcium deficiency in plants.

In the third case, adding Epsom salt to your soil may not help to solve the pH imbalance in your soil.  Epsom salt has a pH between 5.5 and 6.5 (slightly acidic), and you would need a large amount to have an effect on soil pH.

In the fourth and final case, adding Epsom salt to your soil can worsen a nutrient imbalance.  Remember that excessive magnesium in soil can prevent a plant from absorbing calcium.  This will lead to a calcium deficiency and blossom end rot – even if there is plenty of calcium in the soil!

For more information, check out this page from North Dakota State University about how Epsom salt can contribute to blossom end rot.

Disease and Pest Management

Some people believe that Epsom salt can repel pests, and prevent diseases from overtaking your plants.  This is only true to a limited extent.

More specifically, having enough magnesium will allow a plant to produce energy through photosynthesis in order to stay healthy and fight off diseases.

Epsom salt is not a magical cure for diseases and pests if your tomato plant already has enough vital nutrients.  A better way to manage diseases and pests is to practice preventative measures.

If you do encounter disease or pests, remove and destroy infected plants.  Do not put them in your compost pile, since the pests or diseases can winter over in the compost pile and come back to haunt you next year.

Seed Germination Rate and Flowering

Again, Epsom salt will only help with seed germinate rate and flowering to the extent that it can prevent a magnesium or sulfur deficiency in the soil.  It is not a magical method to increase the germination rate for seeds, or to cause plants to produce more flowers.

tomato flower
Phosphorus is a necessary nutrient for plants to produce flowers.

To ensure more flowers on your tomato plants, be sure to add enough phosphorus to your soil via compost, fertilizers, or other methods.  Speaking of which…

Alternatives to Epsom Salt

There are other ways to add magnesium to your garden soil in order to avoid magnesium deficiencies.  Let’s take a look at a few of them now.

Compost

Adding compost to your garden soil will supplement most or all of the necessary nutrients for your tomato plants.  This includes the big three (NPK, or nitrogen, phosphorus, and potassium), along with elements like magnesium, iron, sulfur, and others.

compost bin
Compost will help to restore nutrients and organic matter to your garden. This compost is not quite done yet.

You can put grass clippings, whole or mulched leaves, and fruit or vegetable scraps in your compost pile.  Adding worms to your compost pile will help to break down the organic material even faster.

earthworm
Worms can help to speed up the composting process.

Once the compost looks like nice, black soil, you can add it to your garden (along with the worms!) to supplement the nutrients and organic material that last year’s plants consumed for their growth.

For more information, check out my article on making compost.

Dolomitic Lime

This is an especially good option if your soil pH is a bit low (too acidic).  Dolomitic lime raises soil pH, and as mentioned above, it contains both calcium carbonate and magnesium carbonate.

Thus, it supplements both calcium and magnesium in the soil.  This helps to prevent an imbalance between these two important nutrients, which might occur if you add Epsom salt alone.

Sul-Po-Mag

Sul-Po-Mag, or sulfate of potash magnesia, contains sulfur, potassium, and magnesium.  This can be a good supplement to add if there is already plenty of calcium in your soil, but you need to add either magnesium or sulfur.  It is also useful because it contains potassium, which is necessary for flowering.

Conclusion

Epsom salt can be a helpful short-term garden remedy if you have a magnesium or sulfur deficiency in your soil.  However, there are longer-term ways to maintain the health of your garden soil and plants.

Epsom salt is not a cure-all, and its benefits are often overstated.  Hopefully, you found this article helpful.  If you have any questions, please leave a comment below.

jonathon.david.madore

Hi, I'm Jonathon. I’m the gardening guy (not guru!) who is encouraging everyone to spend more time in the garden. I try to help solve common gardening problems so that you can get the best harvest every year!

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