Ah, Epsom salts. The very thought of them conjures up feelings of healing and relaxation based on the popular Epsom salt bath soaks that are sold in packages with a variety of different herb-enhanced scents.
Today, there’s a lot of chatter about using this fairly common and cheap mineral on our garden plants. THey are often touted to correct nutrient deficiencies and produce bigger plants with more flowers, along with many other claims.
But are Epsom salts really the cure-all they’re touted to be? In this article, we take a look at the use of Epsom salts in your garden. We examine Epsom salt uses in both organic gardening and non-organic gardening.
What Are Epsom Salts?
Epsom salt, also known as magnesium sulfate (MgSO₄), is a naturally occurring mineral that derives its name from Epsom, England, where sources of water in the area are rich with this type of salt.
The history of this salt is that a farmer tried to water his cattle from a pool of water near a spring and discovered that the cattle would not drink the water. He tasted it and found that the water was bitter. An apothecary found out about this source and began promoting the water’s “healing properties.” By 1640, this “medicinal” water was being used as a spa and the rest is… well, history.
Today, it appears that Epsom salts are used mostly for their anti-inflammatory properties. You can take a stroll down one of the self-care and beauty aisles and probably find a bag of scented Epsom salts to use in your bathwater.
How Are Epsom Salts Being Used Currently in the Garden?
There are lots of articles talking about Epsom salts and how they can be used in the garden. People tend to gravitate towards the idea of a cheap, one-size-fits-all scheme. Then you pack that in with the item being a “naturally occurring” mineral. Now you’ve got yourself a winner for the average consumer.
Some of the Epsom salt claims are that Epsom salts can be used to make plants bushier, to help with germination or nutrient uptake, to produce more flowers, to discourage pests. Similar to neem oil in gardening, the list could probably go on. Various articles will recommend applying Epsom salts to your trees, shrubs, tomatoes, roses, and even your lawn.
To be frank, I’ve heard chatter amongst people in the independent garden center industry. How to use Epsom salts is probably one of the least favorite questions folks in the industry get from their customers!
In order to get the skinny on Epsom salt use in the garden, let’s first talk a little science.
The Science of Epsom Salts
Magnesium sulfate, or Epsom salt, is made up of two ions, positively charged magnesium (Mg²+) and negatively charged sulfate (SO42-). If you can’t recall chemistry class in high school, then note that an ion is an atom or molecule with a net charge due to electron loss or gain.
Plants take up all sorts of ions as nutrients and use them to grow and thrive. Magnesium is taken up through the plant and used as the primary constituent of chlorophyll, and without chlorophyll, photosynthesis (the process that helps the plant make sugars) would not occur. This element is also important for protein synthesis and plant metabolism in general.
You’ll see signs of magnesium deficiency on the lower, older leaves first because magnesium is mobile throughout plants. In most plants, you’ll see interveinal chlorosis (yellowing between the veins of the leaves). Leaf tissue will eventually turn brown and die if the magnesium deficiency is severe. Some plants may develop other symptoms, like the lower leaves having a reddish-purple cast.
Deficiencies in magnesium can be caused by many things. First, your soil may be lacking in magnesium. Sandy, acidic soils are most likely to be deficient in magnesium.
Second, excessive amounts of calcium or potassium may also lead to magnesium deficiency in plants. This is because these positively charged ions compete with each other for plant root uptake and attachment to the negatively charged sites in the soil.
Sulfate is a molecule composed of sulfur and oxygen. It’s taken up by plants and used for synthesis of certain amino acids. For some leafy vegetables, plants can become deficient in sulfur. The result can be a buildup of nitrates in the leaves. This reduces food quality. Sulfur is also required for the synthesis of fatty acids and the synthesis of chlorophyll. Additionally, sulfur is a component of the compounds that make the characteristic taste and smell of the mustard and onion plant families.
Sulfur deficiency causes stunted, thin-stemmed, and spindly plants overall. Symptoms occur first in the younger leaves. Sulfur uptake of plants is primarily through the uptake of sulfate (SO42-) molecules. Small quantities of sulfur can be obtained by plants through the uptake of sulfur dioxide (SO2) through the leaves, though too much can be toxic.
Many people believe that the sulfur in Epsom salts can help alter the soil pH. Soil pH is a level that measures the acidity or alkalinity of your soil and ultimately determines what plant nutrients are available to a growing plant. Applications of elemental sulfur (S) can react with soil water to form sulfuric acid (H2SO4), which then acidifies (or drops) the pH level of the soil. However, the sulfate ion in Epsom salts does not react with soil water to form sulfuric acid. Therefore, it has no effect on soil pH.
Epsom Salts and Plant Usage
In the mid-1900s, researchers noticed that many orchards were suffering from a “leaf blotch,” and this was attributed to a magnesium deficiency. For several decades afterward, magnesium sulfate was applied to the soil and leaves of orchard trees. This was solely put into place to correct magnesium deficiency. But further research was inconclusive as to whether this application of magnesium sulfate really helped the problem.
However, because foliar sprays can sometimes produce an immediate positive effect on plants, magnesium sulfate was continuously used to treat this leaf blotch phenomenon. Foliar sprays are a temporary fix, as they do nothing to alleviate soil nutrient deficiencies.
Epsom Salt Application Drawbacks
Epsom salts are just as described – they are salts. An excessive salt application can cause salt injury in plants. Namely browning, dieback, reduced plant vigor, delay in fruit or seed production, and even death.
Excessive use of Epsom salts can also lead to deficiencies in other plant nutrients. Plants may end up deficient in nutrients like manganese, iron, boron, potassium, and calcium. Root colonization of beneficial microbes, like nitrogen-fixing bacteria, can also be reduced due to excessive magnesium sulfate use.
Lastly, excessive amounts of magnesium in the soil can lead to the release of toxic aluminum. This can then be taken up by plants or released into aquatic ecosystems.
Should I Use Epsom Salts on My Plants?
Before making an application of Epsom salts to your garden, you should first ask yourself: What is the goal I’m trying to obtain?
Thinking of using Epsom salts in your garden as a cheap fertilizer source? Then, the first thing you should do is test your soil. There are at-home test kits available, but obtaining analysis from a reputable soil lab is the best way to go.
You can collect a soil sample and ask your local extension office to help you find a soil lab. The lab can test your soil, or you send off a soil sample to a soil lab yourself. The great thing about a soil test is that you will learn your soil pH, organic matter percentage, nutrient levels, and much, much more. Some soil labs will even provide fertilizer recommendations based on the levels of your nutrients in the soil!
Next, if you see that your soil is low on magnesium, then maybe a magnesium sulfate fertilizer application is right for your garden. Remember that a foliar application of magnesium sulfate is only a quick fix.
If you want to increase the magnesium levels in your soil, then you’ll need to make a soil application. There are other fertilizer sources that can add magnesium to your soil as well, so you may consider an application of dolomitic limestone, sulfate of potash magnesia, or magnesium oxide.
Check the fertilizer label to acquiesce magnesium content of the fertilizer you are using. Then, use the fertilizer in accordance with the manufacturer’s instructions. Most commercially made fertilizers that are used for flowers and vegetables are typically balanced in their magnesium content.
The important thing to remember is that you should diagnose what is going on in your garden BEFORE you apply fertilizer of any sort. Choosing a solution before diagnosing the problem will not guarantee intended results.
If your goal is to deter pests, change soil pH, help seeds germinate, produce more flowers, or make plants bushier, then an application of Epsom salts may not help. In fact, it may harm your plants, especially with overuse.
If you are trying to remedy anything besides a magnesium deficiency, then you should consider other factors related to these problems. Is your plant receiving ample sunlight and water? Is your soil compacted and/or draining properly? Have you properly pruned or pinched the plant if needed? Is your soil lacking in any of the macronutrients (nitrogen, phosphorus, and potassium). What is your soil pH and what is the soil pH requirement for the plant(s) you are growing?
In an age where consumers are looking for “natural,” one-size-fits-all remedies for their gardening problems, there’s been a lot of talk about Epsom salt application. The important lessons you should have learned from this article are:
- Do not apply epsom salts to your garden without a soil test first. Send your sample to a reputable soil lab first. Ask your local extension agent to help you read the results if you’re unsure what you’re looking at. Most soils are unlikely to have severe magnesium deficiencies. Though, sandy, acidic soils seem to have the most aptitude for being Mg-deficient.
- If your soil is deficient in magnesium and your plants are displaying magnesium deficiencies, then maybe a magnesium fertilizer is the way to go, whether it is magnesium sulfate (epsom salt) or another magnesium-based fertilizer.
- Foliar sprays do not correct soil nutrient deficiencies, no matter whether the deficiency is of magnesium or another nutrient.
- Epsom salts are not a cure-all for your garden. If you’re looking to deter pests, correct soil pH, help seeds germinate, make plants bushier, or produce more flowers, consider what other factors may be influencing your garden before you apply this “salty” fertilizer. You may end up doing more harm than good.
If you’re interested in learning more about Epsom salts in the garden, Dr. Linda Chalker-Scott has an excellent article published through Washington State University that goes into further explanation of why Epsom salts are not the cure-all for the garden that they’re touted to be. No matter what you apply in the garden, remember to not put the cart before the horse. After all, there’s no need to fix a problem that’s invisible.