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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
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everything that ails our plants. Gardeners tout everything as a
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miracle cure for something in the garden, from putting tums in
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the soil to burying fish, making weed killer out of vinegar and
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salt, please don't do that. To using Dawn dish soap as an
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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
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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.
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Thanks for listening to another episode of the Just Grow
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Something podcast. For more information about
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today's topic and to find all the ways you can get in touch
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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.