I have seen a lot of posts on social media talking about using Epsom salt in vegetable gardens. The claims seem almost too good to be true. Is Epsom salt good for the garden? OR

For starters, the claims are indeed too good to be true. While Epsom salt can be a useful additive to your soil under certain conditions, many of the claims concerning Epsom salt are exaggerated if not completely false. So, let’s try to clear some things up.

Epsom salt is magnesium sulfate which is one of the secondary nutrients we find in healthy soil. If through testing, it is determined that your soil is deficient in magnesium, then Epsom salt would be good to add as a way to correct that deficiency. However, magnesium deficiencies are not common in home gardens.

Magnesium deficiencies are usually found in soil that has been farmed heavily over an extended period of time or perhaps soil that has had nutrients leached out due to heavy rainfall or over-irrigation. In this case, adding magnesium to the soil would be an appropriate strategy to help remedy that deficiency.

One thing that can interfere with your plant’s uptake of magnesium is excessive potassium in the soil. However, adding magnesium will not correct the problem until the potassium issue is corrected. Conversely, soil with too much magnesium may result in a potassium deficiency in your plants because magnesium in excess can interfere with potassium uptake.

The only way to know these levels for sure is to do a soil test through the Tulsa County OSU Extension. We have information on our website (www.tulsamastergardeners.org) on how to do a soil test under the Hot Topics section.

Instead of digging deeper into soil chemistry, let’s look at some of the common claims concerning adding magnesium to your soil via Epsom salt.

Epsom salt helps with seed germination.

All the nutrients a seed needs to germinate can be found within the seed. In fact, seeds can germinate in a wet/damp paper towel. Epsom salt does not factor in to this equation.

Add a scoop of Epson salts in each hole when planting tomatoes to prevent blossom end rot.

Blossom end rot is a pretty common issue in tomatoes during rainy seasons. It is caused by a calcium deficiency and the calcium deficiency is typically caused by irregular watering or excessive nitrogen. Epsom salt will not correct either of these situations and in fact can exacerbate the situation because calcium and magnesium compete for uptake into the plant. So, adding magnesium via Epsom salt may actually contribute to the occurrence of blossom end rot in your vegetables.

Epsom salts should be sprayed on tomato plants to help them grow and encourage a larger harvest of better tasting fruit. 

Unnecessary unless you have a magnesium deficiency.

Epsom salts are highly soluble so you can’t overuse it.

It’s true, Epsom salts are very soluble, but unnecessary nutrients of all kinds, when applied in excess tend to end up as pollutants as they are washed out of the soil and landing in unwanted areas.

Epsom salts help plants grow bushier.

Again, this would be true if you had a magnesium deficiency.

So, what are the signs of a magnesium deficiency in your soil? Magnesium aids in the production of chlorophyll so if your plants don’t have that dark green color, it’s possible you have a magnesium deficiency. But again, this is not very common in home gardens and you would need a soil test to verify this deficiency. Don’t just add magnesium willy-nilly because you may cause more harm than good.

To know for sure if you have an issue with magnesium levels in your soil, get your soil tested. When you bring the sample into the OSU Extension, be sure to tell them you would like to add a test for secondary nutrients. But just know, we rarely find a magnesium deficiency in residential soil tests.

While we’re on the topic of garden myths, many of you have seen recipes online about how to make your own insecticidal soap. Insecticidal soap is a great organic pesticide with very little likelihood for collateral damage to insects if used properly. It’s usually where I start when dealing with a variety of insect pests in my garden.

While the ability to make your own insecticidal soap to save some money can be attractive, store-bought isn’t that expensive. It’s probably one of the least expensive pesticides available outside of a strong stream of water from a hose.

Insecticidal soap is made from potassium salts of fatty acids and water. Most commercial brands are about 1% potassium salts of fatty acids and 99% water. Essentially this is a mixture of a soap and water.

The problem is that the dish detergents generally recommended as an ingredient to make your own insecticidal soap do not contain potassium salts of fatty acids but instead consist of a variety of chemicals such as de-greasers, coloring agents, perfumes, and sudsing agents. All of these work well to help clean and de-grease your dishes but aren’t that great for your plants. In fact, some of these dish detergents may dissolve the waxy coating on your plant’s leaves and that is never good.

The bottom line is, just purchase the commercial insecticidal soap and your plants will have a better chance of living happily ever-after. And save the Epsom salt for your bath. See you in the garden.

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org. Photo: Brenda Kennedy, University of Kentucky, Bugwood.org