Which “Epsom Salts” will help your plants and which will kill them?

“Epsom Salts” used to be the common name for a well known, and well used compound with many uses, including helping your plants. However, as we humans do, we’ve lost our way. Now “Epsom Salts” from one bag might help your plant, and from another bag it might kill your plants. I’m going to encourage you to use the good one (if you actually need it) by explaining what it is and what it does. I’m going to show you how to identify the ones that will kill your plants, and then I’ll show you how to save a whole lot of money.

First, if you need to save some time, this article is also available here as a video on Youtube. (Click the icon below).

In the ground water of Epsom in England there is a substantial amount of a salt called Magnesium sulphate. It can be ingested with medicinal benefits, and applied to the skin (as a bath) for benefits to the skin. (As a rule, don’t ingest anything because an online article says to. Check with your doctor first.) It can also be added to soil to add magnesium and sulphur, both of which are involved in essential biological functions in plants and can be limited in many soils.

Thus, “Epsom Salts” became a heavily used fertilizer (technically an additive) either under the names “Epsom Salts,” “Magnesium sulphate,” or “MgSO4.” At the same time you could by a small bag of “Epsom Salts” at a health or beauty or hardware store in a package that explains all of its real and supposed health benefits. The only difference between the fertilizer and the bath salt was the size and type of the packaging and the price.

Someone made an absolute fortune getting MgSO4 in bulk for pennies, repackaging it and charging a lot. So, if you read no further and just want to save money, don’t buy Epsom Salts from a health, beauty or hardware store and instead buy it in bulk from a landscape or fertilizer retailer. And this could further prevent you from making the mistake below:

What is an “Epsom Salt” is far more complicated now. If you insist on buying it in a small package somewhere, check the ingredients. If you are going to use it for your plants IT MUST BE Magnesium sulphate (MgSO4.) Take a look at these two packages and their ingredients; both are “Epsom Salts.” The one on the right is actually Magnesium Sulphate (with added fragrance…not sure what that does to plants.) The one on the left is (take a look at the ingredients) sodium chloride…. also known as table salt. Do not make a catastrophic mistake and apply the wrong soil additive.

Let me stop to remind you I’m not selling anything, and I am not criticizing the companies above. These products are simply not designed for plant use. And since “Epsom salts” was the common name given to Magnesium Sulphate collected in Epsom, if other salts (like table salt) are collected there too, then I guess they are epsom salts. My point: the Epsom salts used for plants and packaged for growers/gardeners should include proper mix ratios and technical data. So, again….don’t confuse these two, and please share this information.

Magnesium is involved in essential tasks like photosynthesis. It also is involved in stabilizing the uptake or retention of other micronutrients. Can you over-do it? Hell yes. Remember, like all fertilizers, this is a salt – (not table salt, but) a “salt” according to chemistry. Salts can build up and should be regularly flushed from potting soil with pure water or washed out with rain water, otherwise you roots can burn. Magnesium is a metal, so while it can help if your soil is limited in magnesium, too much can prevent uptake of some micronutrients, and you won’t be able to get it out of your soil. You should always test your soil and only provide soil additives as necessary.

Sulphur is also essential for plant functions. Interestingly there is research being done right now that is suggesting that increased sulphur uptake can strengthen plant tissue against infections like Powdery Mildew. Of course, sulphur is often used to decrease pH in soil, so soil should be tested for sulphur as well.

If you’ve ever wondered why there are so many fertilizers and formulations here’s a bit of info you might find interesting. Many commercial growers will switch fertilizers as often as daily. Each fertilizer will have its own mixing tank and injector. And that’s because certain fertilizers can bind together, precipitate and clog up the equipment. This prevents the actual fertilizer mix needed and what does get through to your plants might be missing certain micro or macro nutrients.

For example, I’m familiar with a grower who will provide a rapid water soluble fertilizer (20-20-20) for two days and then switch to Magnesium Sulphate for two days. (To counteract the rapid growth by firming up plant tissues.) In the MgSO4 they provide micronutrients as well. They do not mix the 20-20-20 with the MgSO4 because it would “gum-up.”

So what I hope to achieve by explaining this is that when you grab an off the shelf fertilizer you’ll likely be grabbing one that is “complete” and specific to the types of plants you want to grow. But you should still be taking the due-diligence to test your soil, and see if the “complete” fertilizer will top up any specific soil deficiencies. If possible, just work on the deficiencies first, you may find your outdoor soil isn’t that bad!

Lastly, compost. Everything you put into the garden stays there, except for what is harvested or taken elsewhere by animals and leeching (through rain water). Many micronutrients, and even macronutrients will be taken up by plant material and then enter the food chain in the compost. When you return that to the garden you still have most of the micros and macros but they’ll be present in more complicated and slower-released forms….and this benefits your plants. That slow, healthy growth is natural. It better resists pest and pathogen damage and creates more robust plants. But providing some additives (especially metals) can be a near permanent addition. You can interfere with plant growth by providing additives that aren’t needed.

Lastly, I’m usually the person that says “don’t get Epsom Salts,” because in so many cases people are just using it as a “wonder drug” for plants. It has a very specific function and purpose and is not as often needed as many would guess. So, be careful. Start natural, test your soil and amend only when necessary.

I hope you’ve found this helpful. And if nothing else, please tell your friends to be careful which “Epsom Salts” to buy.

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