If you are in any gardening group, whether an in-person club or online, you likely see countless home remedies for everything that ails our plants. Gardeners tout everything as a miracle cure for something in the garden, from putting tums in the soil to burying fish, making weed killer out of vinegar and salt (please don’t) to using dawn dish soap as an insecticide (again, please don’t).
One that pops up over and over again is using Epsom salts, either sprinkled or added to the soil or used as a foliar spray when diluted in water. I’ve seen it recommended for blossom end rot, boosting plant growth, germinating seeds and other random maladies. But, is it really good for your plants? Does it help with any of that stuff or is it just another case of correlation over causation?
Today on Just Grow Something we’re digging into Epsom salts. What they are, if they can help in the garden, and, if so, with what exactly. That way next time someone recommends Epsom salts for curing the yellowing leaves on your plant you’ll be able to decide for yourself whether that’s an effective plan. Let’s dig in!
References and Resources:
Ep. 18 - Garden Talk Tuesday: Plant Nutrients and Why You Need to Know Them
Ep. 22 - Garden Talk Tuesday: Plant Nutrient Deficiencies and Toxicity
Focal Point Friday: Plant Nutrient Basics
Fertilize with Epsom Salts - Garden.org
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If you are in any gardening group, whether an in person club
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or online, you likely see countless home remedies for
00:00:06
everything that ails our plants. Gardeners tout everything as a
00:00:10
miracle cure for something in the garden, from putting tums in
00:00:13
the soil to burying fish, making weed killer out of vinegar and
00:00:16
salt, please don't do that. To using Dawn dish soap as an
00:00:21
insecticide Also, please don't do that.
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One that pops up over and over again is using Epsom salts,
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either sprinkled or added to the soil, or used as a foliar spray
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when diluted in water. I've seen it recommended for
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blossom and rot, boosting plant growth, germinating seeds, and
00:00:38
all kinds of other random maladies.
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But is it really good for your plants?
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Does it help with any of that stuff, or is it just another
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case of correlation over causation?
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Today on Just Grow Something, we're digging into Epsom salts.
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What are they, if they can help in the garden, and if so, with
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what exactly? That way, next time someone
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recommends Epsom salts for curing the yellowing leaves on
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your plant, you'll be able to decide for yourself whether
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that's an effective plan. Let's dig in.
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Hey, I'm Karen, I started gardening in a small corner of
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my suburban backyard and now 18 years later, I've got a degree
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in horticulture and operate a 40 acre market farm.
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I believe there is power in food and that everyone should know
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how to grow at least a little bit of their own.
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On this podcast, I share evidence based techniques to
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help you plant, grow, harvest and store all your family's
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favorites. Consider me your friend in the
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garden. So grab your garden journal and
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a cup of coffee and get ready to just grow something.
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I just finished a lovely conversation with Amy over at
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the Grounded in Maine podcast. We had a great time talking.
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I think that episode is going to come out next week.
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So I encourage you to go and follow her podcast.
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She talks all things sustainability with a whole
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bunch of different people and it was really a very fun
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conversation. So the first thing that we need
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to define is what is an Epsom salt?
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It's not actually a salt, thankfully, because like I
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alluded to when telling you not to use that homemade weed killer
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that has all the salt in it. Yeah, because too much salt in
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our soil is a bad thing. No, Epsom salts are not actually
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salt. So what are they?
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Epsom salts are magnesium sulfate, which is made-up of two
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things that plants do need, magnesium and sulfur.
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These are secondary nutrients, the type of nutrients that are
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needed in moderate amounts compared to the primary
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essential nutrients like nitrogen, phosphorus and
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potassium. Magnesium in plants plays an
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essential role in photosynthesis, that process
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that plants use to make energy for growth.
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Also protein synthesis which is necessary for cell formation,
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activation of plant enzymes needed for many cellular and
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growth functions, and chlorophyll synthesis, that
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green pigment in plants that is essential for optimum plant
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growth. Sulphur is used in our plants
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also for the development of chlorophyll, which improves
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photosynthesis and the growth rates, increased resistance to
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pests and diseases, and helps produce necessary enzymes and
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plant proteins within the plant. In fact, some plants like
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mustard, onion, garlic and broccoli need adequate sulfur to
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produce their flavors. Now if you want a refresher on
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macro, secondary and micro or trace nutrients, I will link to
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episodes in the show notes where we talked all about those plant
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nutrients in depth. So if magnesium helps increase
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intake of phosphorus, which is great for flowering and
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fruiting, and it boosts production of chlorophyll,
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giving a healthy green color to the plant leaves and encouraging
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absorption of CO2, then using Epsom salts on our plants should
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be a good thing, right? A lack of magnesium can
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contribute to an overall anemic appearance in your plants.
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In fact, magnesium deficiency is first seen as intervenal
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chlorosis. So that is the yellowing of the
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leaf tissue that is between the veins of the older leaves.
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Usually when gardeners are talking about Epsom salts,
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they're talking about tomato plants.
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So we'll just use that as an example.
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When tomato production or with tomato production, it is widely
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known that calcium levels in the soil are important for
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prevention of blossom and rot, that ugly little scarring that
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happens, or rotting that happens on the bottom of the fruit at
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the blossom point that makes the fruit pretty much inedible.
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So tomato gardeners have always focused on making sure that
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there is enough soil calcium or maybe too much calcium in the
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soil sometimes to prevent this from happening.
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Another nutrient, another one of the primary nutrients, potassium
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is also important for plant and fruit quality and for regulating
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water movement within the plant, plus a whole bunch of other
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really important functions. Now, even though blossom and rot
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resulting from calcium deficiency can cause those
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tomato fruits to be inedible, if we have a magnesium deficiency,
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it can reduce the overall plant health.
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And ultimately you are going to have lower quality fruits and
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you're gonna have fewer of them. And then if we have low
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potassium in the plant, that can make the plant less tolerant of
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heat and drought stress, which obviously we're growing tomatoes
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in the hot the heat of the summer.
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So we want it to have those qualities.
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But here is the kicker. Calcium and potassium and
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magnesium compete with each other for being taken up into
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the plant, and whichever one is more abundant in the soil is
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actually going to be taken up by the plant more readily than the
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other two. Which means that you can end up
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with an imbalance or even worse, a downright deficiency in the
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plant even if there are adequate levels of all of those nutrients
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in your soil. I mean, who knew plant nutrients
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were so fussy, right? So if someone says to use Epsom
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salts on your tomato plant because you've got blossom and
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rot, well, take note. An overabundance of magnesium
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can actually harm your soil and hinder your plants.
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And since magnesium actually hinders calcium uptake, not only
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would it not prevent the blossom N rot, it could actually 'cause
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it calcium can be notoriously slow to move.
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So the more magnesium you have, the less likely the plant is
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going to get enough calcium. Now, secondarily to this, if you
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have too much magnesium in your soil and it's not taken up in
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the plant, it has to go somewhere.
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So either it's gonna leach into the groundwater and end up
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elsewhere in your garden or your yard, or it's gonna settle into
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the water table and eventually end up in a river or a stream.
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And that can upset, you know, the ecosystem.
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So then this goes for any mineral or nutrient that is
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applied in excess inner gardens. So just be mindful of that when
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you're adding anything to your garden or to your yard, make
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sure that there is a need for whatever it is that you're
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applying. So if you see signs of a
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magnesium deficiency in your plants, like those yellowing
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leaves with the intravenal chlorosis we talked about, then
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yes, you can use Epsom salts to help correct that problem.
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But the best way to do this is by creating a foliar spray of
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about 2% Epsom salts to water, so maybe one or two tablespoons
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per gallon of water, and not by applying it to the soil.
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So by doing it as a foliar spray, you're going to prevent
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the magnesium from building up in the soil and interrupting the
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uptake of the calcium or the potassium.
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This is also a good solution if you see signs that your plants
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are low in phosphorus, even though your soil test shows that
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you have plenty of it in the soil.
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Remember, magnesium helps with phosphorus absorption, so if
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you're seeing stunted growth, delayed maturity, poor root
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development, small leaves, or just sort of random defoliation
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and your soil test looks good, then try an Epsom salt spray.
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Don't just use it because you want to see more lush growth
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though. More isn't always better.
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Using it without cause can result in too much leafy growth.
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And unless you're growing something specifically for its
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leaves, like lettuce or kale or something like that, too much
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leafy growth can take resources away from fruit production.
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So use the Epsom salt spray judiciously, just like anything
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else. See the signs, react
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accordingly. Don't just spray and hope it
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works, because you might cause more harm than good.
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So that's the magnesium in Epsom salts.
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What about the sulfur? Remember, chemically, Epsom salt
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is hydrated magnesium sulfate. So it's about 10% magnesium and
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about 13% sulfur. Sulfur is a key element in plant
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growth. It is critical to the production
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of vitamins and amino acids and therefore protein and enzymes.
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It is also the compound that gives vegetables like broccoli
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and onions and garlic their flavors.
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Now, sulfur is very seldomly deficient in most garden soils
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here in North America because it gets it from the rain it's used
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in or it gets it from the commonly used animal manures
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that we use in compost. Those all contain sulfur.
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And if you're using any kind of a chemical fertilizer like
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ammonium sulfate, there is plenty of it in there.
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So we're not usually deficient in the soils.
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Of course, that doesn't always mean that our plants are taking
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up that sulfur in adequate amounts.
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So it's good to know what a sulfur deficiency looks like
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because there can be situations that prevent the the plant from
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taking up the sulfur. So if you have pale green,
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yellowish green or completely yellow leaves, similar to a
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nitrogen deficiency, but you're gonna see it in the younger
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leaves first, those top leaves, not the older ones.
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You might see stunted growth, reduced yields, smaller than
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usual leaves that have like a bronze or a purple tint to them.
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And then they do this sort of leaf cupping on the new leaves
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that there is a sulfur deficiency.
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So if you see sulfur deficiency, again, a foliar spray is going
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to be most effective here for quick absorption.
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Or you could water the plant with one or two tablespoons of
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Epsom salt in a gallon of water, provided that you are not
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worried about it interrupting the calcium uptake.
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Now, what about the claim that Epsom salts help with seed
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germination? OK, the best way to explain this
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is how one of my plant professors described a seed and
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I have always used this terminology ever since.
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A seed is a baby plant in a box with a sack lunch.
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OK? In other words, the plant that
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will sprout from that seed has everything it needs inside the
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seed casing to feed itself while it sprouts.
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Most seeds don't need any external nutrients in order to
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germinate. In fact, most seeds contain
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enough essential minerals to initiate both root and shoot
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growth just by being placed in a moist paper towel.
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That being said, magnesium is one of those nutrients that is
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essential for seed sprouting, so it stands to reason that once
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the seed coating is penetrated by the water in the soil, then
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an extra boost of magnesium would help that seedling sprout
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out of the soil faster. If you've had difficulty getting
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seeds to sprout with strong growth in your indoor seed
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starting set up, which is likely caused by soil conditions like
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incorrect temperature and moisture, then the addition of
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Epsom salts to the seed starting mixture may give them a boost.
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But if you've successfully sprouted seeds without any help
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in the past, then there is absolutely no reason to start
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using Epsom salts now. That's the sciency stuff, right?
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Epsom salts may be helpful on plants that are grown in soils
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that are slightly deficient in magnesium, maybe the more
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alkaline soils, because that high pH could actually slow the
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movement of certain nutrients. Or if you have very acidic, like
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low pH soils where there's going to be a natural magnesium
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deficiency. And then maybe soils that are
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naturally high in calcium and potassium, where the magnesium
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just can't compete for uptake into the plant.
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Gardeners in informal ad hoc studies who have tested using an
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Epsom salt spray in Peppers and tomatoes and roses often swear
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that the leaves are more lush, which I totally believe, and
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that the fruits were bigger than without the Epsom salts.
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But there are very few controlled studies, with the
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exception of onions, that have been able to definitively show
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the direct benefits of using Epsom salts and often times has
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actually been shown to be detrimental to plant growth.
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Why? Well, because of all the other
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variables in the soil such as the pH and the calcium and
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potassium content and the weather and anything else that
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may affect plant growth. They've even tested in
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hydroponic situations where everything was carefully
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controlled and been unable to reproduce favorable results
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consistently, where the Epsom salts were proven to be the
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catalyst. And for the onions, well, my
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best bet is the improvement was due to the sulfur in the Epsom
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salts. So just like anything in the
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garden, whether or not it works will depend on your garden, your
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soil, your weather, your crop. Just use any home remedy
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sparingly and only when you see signs that your plants need it.
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Until next time, my gardening friends, keep on cultivating
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that dream garden, and we'll talk again soon.
00:14:44
Thanks for listening to another episode of the Just Grow
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Something podcast. For more information about
00:14:49
today's topic and to find all the ways you can get in touch
00:14:52
with me or support the show, go to justgrowsomethingpodcast.com.
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Until next time, my gardening friends, keep learning and keep
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growing.