Is Epsom Salt Good or Bad For Tomato Plants?

Trying to figure out if you should put some epsom salt on your tomatoes in your garden this season, but aren't sure if epsom salt is good or bad for tomatoes? In this article, suburban homesteader and gardening expert Merideth Cohrs examines the controversial topic of using epsom salt when growing tomatoes.

epsom salt for tomatoes

Tomatoes are iconic for the home gardener. The plants are beautiful, and garden grown tomatoes are more delicious than anything you’ll find in the grocery store. Beyond that, it is so satisfying to pull a cherry tomato off the vine and pop it in your mouth, slice up a homegrown heirloom beefsteak, or cook a beautiful pasta sauce from Romas grown on your deck. Yes, my friends, tomatoes are awesome.

It’s no wonder then that myths abound in the gardening world on how to ‘hack’ the growth of your tomatoes. The most common seem to circulate around the benefits of coffee grounds, eggshells, and (you guessed it!) Epsom salt.

Years ago as a new gardener, I remember multiple people telling me to add Epsom salt into the soil before planting my tomatoes. I also remember hearing about them being a miracle cure for the dreaded blossom end rot. But are Epsom salts really effective at helping your tomatoes thrive? Let’s take a look!

The Short Answer

The short answer is that Epsom salts are incredibly good for your tomato plants in certain cases when your tomatoes are dealing with a magnesium deficiency, but are completely ineffective in others. Let’s dive in deeper!

A Brief Overview

Adding nutrients to garden soil
Epsom salt can help tomatoes in a few different ways.

First, let’s understand what Epsom salt is, and how it’s used in the garden. When I was a kid, I remember my dad using it in the bath, but beyond that, I never really knew anything about it.

Here’s a little history and science lesson for you all rolled into one. Epsom salt is one of many naturally occurring mineral salts that contain a compound of magnesium and sulfate. The name Epsom is an honorific to the town of Epsom, England where the salt was originally discovered about 400 years ago.

While it looks a lot like table salt, you shouldn’t ever consume Epsom salt. Instead, you can use it in a bath to relieve stress or loosen sore muscles. You can also use it as a garden supplement in some cases.

The Long Answer + Myth Busting

So, ready to learn even more about epsom salts and tomato plants? If you start digging in and doing research online, you’ll get plenty of opinions on whether or not it’s actually good for tomato plants or not. Many of these opinions lack firsthand experience.

But does using epsom salt on your garden tomato plants actually get backed up by science? Or are they just another horticultural myth? The answer is actually a bit of both. Let’s take a deeper look at the common ailments that can get fixed when applying this somewhat controversial mineral to your tomatoes.

It Fixes Yellowing Leaves

yellow tomato leaves
It can help prevent the yellowing of tomato foliage, as magnesium is part of the chlorophyll molecules.

Seeing our prized tomato plants in distress is always upsetting. Any time your previously healthy tomato starts to develop yellowing leaves, we can panic a little.

There are a number of reasons why your tomato leaves may be yellowing – over or underwatering, transplant shock, soil compaction, nutrient deficiency, pests, or disease – and most are relatively benign and easy to fix.

In this particular case, when yellowing leaves are the result of magnesium deficiency, you will notice a very specific yellowing of the leaves. The veins of the leaf remain green while the rest turns a light shade of yellow. This mottled appearance is a telltale sign that your tomato plant is unable to produce chlorophyll correctly and is in desperate need of magnesium.

As we recently learned, magnesium is a main component in Epsom salt, and its application can quickly combat magnesium deficiency and help your tomato recover quickly.

The best way to apply it in this case is as a foliar spray, meaning we will be spraying the leaves directly. Mix one tablespoon in a gallon of warm water (to help the salt dissolve) and liberally spray the leaves and stem.

After the entire plant has been misted, you can water the soil with the remainder. The best time to spray is in the morning so leaves have time to dry and absorb the spray before the sun can cause any burning.

Myth or Fact?

Fact! Epsom salts are a great way of adding magnesium directly to your tomatoes and to the soil. Invest in a soil test kit so that you can ensure your tomatoes are getting the right amount of nutrients throughout the growing season.

Magnesium levels should be primarily provided by fertilizers used at the time of planting and then every 2 weeks once your tomato starts fruiting. But using it as a diluted foliar spray is a great ‘as needed’ trick!

It Improves Flavor

Beautiful red tomatoes grows in the garden
Epsom salt can improve the decorativeness of the crop and the fruit flavor.

Flavor is a pretty important consideration when it comes to growing tomatoes. If you want a bland, flavorless tomato, buy them from the store! A solid mix of micronutrients including magnesium and sulfur plays a large role in both the overall health of your plant, as well as the flavor of the tomatoes.

Proper and consistent fertilization goes a long way toward helping your tomatoes get large, juicy, and full of flavor, but the occasional dash doesn’t hurt either! Foliar spraying is a great way of boosting micronutrient absorption in your tomatoes, but you can also just add a small amount to your watering can.

The ideal solution for maintenance is one tablespoon per foot of plant height. Break that up into two watering applications per week, and your tomato plant will have all those micronutrients readily available. You’ll have the tastiest tomatoes in the neighborhood come harvest time!

Myth or Fact?

Fact! Adding Epsom salts to your plant either through foliar spray or direct watering is a great way of boosting micronutrient absorption.

This helps your tomato plant produce large, juicy, and very sweet fruits. Remember that a little bit goes a long way and too much can cause more problem than it fixes.

It Prevents Blossom End Rot

Tomatoes damaged by Blossom End Rot
Epsom salts do not prevent blossom end rot in tomatoes.

When I first experienced blossom end rot in my tomatoes, I was told to liberally add Epsom salt to the soil to mix the problem. But was that good advice?

Blossom end rot is a condition that causes the fruit of tomato plants to turn brown and rot from the bottom. This happens when the plant is unable to bring up enough calcium through the roots, causing the plant to become deficient in that micronutrient. It’s really upsetting when you see this happening in your tomato plants because the affected tomatoes are a total loss.

Calcium deficiency is caused by one of three things:

  • Lack of water or uneven watering
  • Calcium deficiency in the soil
  • pH imbalance in the soil
  • Nutrient imbalance in the soil

You can see that blossom end rot has nothing to do with magnesium. It also doesn’t necessarily mean there is a problem or deficiency in the soil at all.

In the first case, this is 100% about your watering habits. Adding magnesium will not change the water content in the soil. In the second case, a calcium deficiency is not going to be fixed since there is no calcium content whatsoever.

In the third case, there are easier and safer ways to adjust the pH of your soil. Epsom salt is only slightly acidic at a pH of 5.5-6.5 and you would have to add a large amount to make a difference. This would cause more problems than it would fix!

In the fourth case, this is where adding Epsom salt can actually be harmful and cause a worse case of blossom end rot. Remember, it’s mainly composed of magnesium.

If your tomatoes take up too much magnesium, it can actually compete with the absorption of other micronutrients like calcium. This will, of course, result in even less calcium absorption than before and probably cause even more causes of blossom end rot.

Myth or Fact?

Myth! Adding Epsom salt to help with blossom end rot is completely ineffective and can actually cause the problem to worsen. Instead, focus on consistent watering habits, pick off the affected fruit, and see if the problem rectifies itself. If not, go ahead and test your soil for calcium deficiencies or a pH imbalance.

It Deters Pests

slug pest on tomato fruit
In fact, Epsom salt is not able to repel tomato pests.

It seems to me that if even a small percentage of pest deterrent advice worked, we would never have to deal with pests in our gardens ever again. Hundreds of myths abound in the natural pest remedy world.

Nine times out of ten, the author or company ‘educating’ you on their efficacy virtually guarantees that they will solve your pest problem. While some natural remedies do work, most you find online are total garbage. Unfortunately, Epsom salt falls into that category.

There has been plenty of research looking into whether it acts as a tomato pest deterrent or repellant for aphids, hornworms, grasshoppers, whiteflies, and a host of other pests. To date, there has been zero evidence to support that it has any effect.

Myth or Fact?

Myth. Epsom salt has no effect on either deterring or eradicating pests in your garden. Focus on tried and true remedies for a pest infestation and, better still, focus on prevention through strong biodiversity in your garden!

It Improves Nutrient Uptake

Cherry tomatoes grow in the garden
It can improve the absorption of nutrients if your soil is magnesium deficient.

A balance of nutrients and micronutrients are critical to the health, growth, and fruit production of your tomato plants. The best fertilizers for tomatoes have macronutrients like nitrogen, phosphorus, and potassium, and micronutrients like magnesium, calcium, sulfur, and zinc.

Here’s a little cheat sheet on the macros your tomatoes need:

  • Nitrogen. Promotes foliage growth. Too much will lead to very bushy plants with little to no fruit.
  • Phosphorus. Crucial for the growth and development of roots as well as fruit. Very important in both the initial stage of growth as well as the final stage of fruiting.
  • Potassium. Helps the plant grow rapidly and produce flowers and fruit. Also important to efficient photosynthesis and tolerance for some tomato diseases.

Micronutrients like magnesium and sulfur are needed in really small amounts, but if they are lacking, your tomato can become stressed. This can inhibit the absorption of the macronutrients that are critical to so foliage growth, strong root development, and fruit production.

If your soil is deficient in micronutrients (you can check this with a soil test kit), the application of Epsom salt can improve the uptake of those important nutrients and improve the overall health of your plant. You can apply it directly to the soil at the time of planting, through the foliar spray, or while watering as discussed earlier.

Myth or Fact?

Fact, sort of. Adding Epsom salt to your soil or plants will only improve nutrient uptake if there is an existing micronutrient deficiency in magnesium or sulfur. If there is such a deficiency, adding it can definitely have a positive impact!

It Helps Speed Up Germination

Tomato seedling in the morning light
Epsom salts have absolutely no effect on tomato germination rates.

Germination is the sprouting of a seed after a period of dormancy. It’s then precipitated by the absorption of water, the passage of time, warmth, oxygen, and light exposure. Put simply, germination is when a tiny seed decides to wake up and create new life.

When you see it written out like that, the germination of a tomato seed seems pretty special. And I can assure you that you will be delighted when you first see that green sprout break free of the soil!

All you really need for successful tomato germination is moist seed starting soil, warmth (I love using a heating mat for germination), and a little time. Seeds are programmed to do all the heavy lifting as long as they receive that basic support from you.

So do tomato seeds benefit from the addition of Epsom salt during germination? That’s a solid NOPE. The addition of extra magnesium during this process is completely useless, so go ahead and just let your tomato seeds do their thing!

Myth or Fact?

Myth. The addition during the germination phase is completely useless. There is no point in adding during any part of the germination process, and it may in fact harm your plant.

It Improves Growth and Vigor

Beautiful tomatoes grows in the garden
Sulfur stimulates the growth of strong tomato plants and promotes the efficient absorption of nitrogen.

As gardeners, we all strive to grow healthy, vigorous plants that produce fruit at prolific rates. I, for one, cannot seem to get enough tomatoes. Each year, I plant more and more plants because I love them fresh off the vine, on sandwiches, in salads, and cooked into sauces.

So if there is something that improves the growth and vigor of my tomatoes, I’m onboard! But does adding Epsom salt make a difference?

Remember, the growth, vigor, and overall health of your tomatoes rely on a balance of macro and micronutrients. Too much of one or not enough of another can cause problems. This is certainly true for magnesium. Without it, your tomato cannot properly photosynthesize and process sunlight into chlorophyll. This will result in stunted growth, yellowing leaves, and a lack of fruit.

Adding Epsom salt when this happens is a great idea. You can apply it to the plant directly as a foliar spray or while watering. Reference the earlier section on yellowing leaves where we talked about proper amounts needed to do this.

Myth or Fact?

Fact. As we have learned before, the magnesium in Epsom salt can be a great boon to a plant that is deficient in it. This can certainly help restore vigor to a plant that had been hurting.

It Is a Great Tomato Fertilizer

Tomato Fertilizer
Epsom salts don’t have much use as a substitute for fertilizer.

Remember when we talked about nutrient uptake earlier? We discovered that tomatoes need a specific balance of macronutrients like nitrogen, phosphorus, and potassium. They also need a balance of micronutrients like magnesium, calcium, sulfur, and zinc to be healthy.

This balance actually changes during the different phases of your tomato plant’s growth cycle. For example, tomatoes need more nitrogen in their early weeks for optimal foliage growth. As the plant matures and sets fruit, it requires more potassium and phosphorus.

Micronutrients are also critically important but are needed in much smaller doses. So while it sort of sounds like it might make a good fertilizer, it would only be helping out with magnesium and sulfur. It wouldn’t do anything for all the other critically important nutrients your tomatoes need.

Myth or Fact?

Myth. Epsom salt will not provide your tomatoes with all the nutrients it needs to grow and produce fruit. Instead of trying to use it as a fertilizer, apply it only when you know there is a magnesium deficiency in your plant.

Final Thoughts

Of the eight myths we looked at in this article, four of them were considered facts. I have to caveat each of those, however, that the benefits of adding Epsom salt to your tomatoes in those cases only make sense if they are truly magnesium deficient. As we discovered, when that happens, it can be very beneficial.

But, if your soil or tomato plants are not magnesium deficient and you add it thinking you’re doing the right thing (or if you add too much), you can actually harm your plant. Overuse can cause root problems in your tomatoes. It can also result in a build-up of magnesium in the soil that causes an imbalance of micronutrient absorption.

Always use a soil test before using Epsom salt on your tomatoes. And in all honesty, if you are fertilizing correctly throughout the growing season, you shouldn’t need to add an outside source of magnesium at all. I hope this was helpful to either prove or debunk myths around Epsom salt use for your tomatoes. Happy growing!

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