How to Use Epsom Salt for Plants

You’d never put table salt on plants, which would kill them. Rock salt from icy roads damages plants, too, and so does the salty spray that comes off the ocean in coastal areas. But many gardeners believe Epsom salt can help plants if you know how and when to use it.

What is Epsom Salt?

Also known as magnesium sulfate, Epsom salt is a compound of sulfur, oxygen and magnesium. While it might look like table salt, it’s not the same, and it tastes bitter. It’s a vital trace element, or micronutrient, that occurs naturally in the soil and helps plants absorb other nutrients.

Humans use Epsom salts, too. Some put it in bath water because it’s believed to relieve muscle soreness and other ailments. Others dissolve it in water and drink it to treat various problems. While some of these uses may be valid, there’s no strong scientific evidence behind most of them.

Do not consume Epsom salt without checking first with your health care provider. If you are pregnant, have kidney problems, skin infections, skin inflammation or other issues, you should also avoid Epsom salt baths.

Epsom Salt for Plants

Aside from the anecdotal evidence about human benefits, Epsom salt does seem to help plants. Generations of gardeners have said it helps their plants grow bushier, produce more flowers and have better color.

It’s also said to help seeds germinate and repel slugs and other garden pests. But unless your soil has a magnesium deficiency, the University of Minnesota Extension Service recommends against adding Epsom salt. Too much can harm your plants and soil.

When To Use Epsom Salt on Plants

How do you know if your soil is low in magnesium? It can become depleted (unless you keep adding more before your plants can use it up). Before you add Epsom salt for plants, send your county extension service a sample of your garden soil for testing and tell them what you’re looking for.

Instead of trying to send soil samples from potted plants, look for signs of nutrient deficiencies. For example, a plant that turns greenish-yellow or yellow all over probably needs sulfate.

A plant with leaves that turn yellow between the veins, while the veins stay green, might need more magnesium. That's called interveinal chlorosis. It can be hard to pinpoint the exact cause of problems because other factors like soil pH and weather also play a role, but your extension service agent can help.

What Plants Don't Like Epsom Salt?

Some plants don’t like Epsom salt because they just don't need much magnesium or they're already getting enough from the soil. These include:

• Beans and leafy vegetables
• Coniferous trees
• Tropical palms don’t like Epsom salt, either.
• Insect-eating plants such as Pitcher plants, sundews and Venus flytraps are other plants that do not like Epsom salt. They’ve adapted to growing in poor soils and even a little can kill them.

Epsom Salt for Tomato Plants and Other Plants

What plants can you put Epsom salt on? Plants like peppers, tomatoes and roses like magnesium, but again, test your soil before adding it. Some gardeners blame a lack of magnesium for making tomatoes taste bitter, but too much can be especially harmful to them. Others swear by using Epsom salt on tomato plants to avoid blossom end rot, although this is controversial.

According to a North Dakota State University horticulturist and other sources, it's a myth that Epsom salt can prevent blossom end rot. Reportedly, additional magnesium can actually increase the chances of blossom end rot in tomatoes.

Can I Just Sprinkle Epsom Salt on Plants?

Never apply Epsom salt straight from the package. Always dilute the granules in water first, and either drench your plants’ roots or spray it on the foliage. Don't spray on hot or sunny days, however, to avoid scorching the foliage.

Will Epsom Salt Kill Weeds?

Highly concentrated amounts of Epsom salt will kill weeds; some people mix it with vinegar for a more potent solution. But you have to be careful. Epsom salt water can harm nearby plants if they absorb it through their roots or, if you’re spraying, if the mist lands on them.

How Much Epsom Salt Do You Put in a Gallon of Water?

You can find many different formulas for applying Epsom salt to plants. The easiest way to use it is to put some in your watering can one or two times a month, using one tablespoon of Epsom salt per gallon of water. If you water often, use one tablespoon per gallon.

You can also use Epsom salt as a foliar spray. Use 2 tablespoons per gallon of water once a month.

If you want to be more precise, the Epsom Salt Council suggests using these amounts:

Houseplants — Apply 2 tablespoons of Epsom salts per gallon of water once a month.

Shrubs (evergreens, rhododendrons and azaleas) — Use 1 tablespoon of Epsom salt per 9 square feet and slowly pour it over the root zone, allowing it to soak in, every two to four weeks.

Lawns — Evenly spread 3 pounds of Epsom salt per 1,250 square feet of lawn or dilute it with water from a sprinkler system or garden hose.

Trees — Spread 2 tablespoons per 9 square feet over the root zone three times a year.

Bare root roses — Before planting, soak the bare root roses in 1 cup of Epsom salt per gallon of tepid water. Add a tablespoon of Epsom salt to each hole when you plant.

Established roses — Apply 1 tablespoon per foot of plant height every two weeks and water it in.

New gardens — Sprinkle one cup of Epsom salt per 100 square feet over the soil and mix it in before you plant.