Epsom Salts - Magic or Myth? - Ep. 206

[00:00:00] If you are in any gardening group, whether in 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

[00:00:12] tums in the soil to burying fish, making weed killer out of vinegar and salt – please don't do that – to using Dawn dish soap as an insecticide. Also, please don't do that. One that pops up over and over again is using Epsom salts, either sprinkled or added

[00:00:29] to the soil or used as a foliar spray when diluted in water. I've seen it recommended for Blossom and Rot, boosting plant growth, germinating seeds and all kinds of other random maladies. But is it really good for your plants? Does it help with any of that stuff?

[00:00:44] Or is it just another case of correlation over causation? Today on Just Grow Something, we're digging into Epsom salts. What are they? If they can help in the garden and if so, with what exactly?

[00:00:56] 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. Hey, I'm Karen. I started gardening in a small corner of my suburban backyard and now 18 years later

[00:01:13] I've got a degree in horticulture and operate a 40-acre market farm. I believe there is power in food and that everyone should know how to grow at least a little bit of their own. On this podcast, I share evidence-based techniques to help you plant, grow, harvest

[00:01:27] and store all your family's favorites. Consider me your friend in the garden. So, grab your garden journal and a cup of coffee and get ready to just grow something. I just finished a lovely conversation with Amy over at the Grounded in Maine podcast.

[00:01:51] We had a great time talking. I think that episode is going to come out next week, so I encourage you to go and follow her podcast. She talks all things sustainability with a whole bunch of different people and it was really a very fun conversation.

[00:02:04] The first thing that we need to define is what is an epsom salt? It's not actually a salt, thankfully because like I alluded to when telling you not to use that homemade weed killer that has all the salt in it.

[00:02:18] Yeah, because too much salt in our soil is a bad thing. No, epsom salts are not actually salt. So what are they? Epsom salts are magnesium sulfate which is made up of two things that plants do need magnesium and sulfur.

[00:02:37] These are secondary nutrients, the type of nutrients that are needed in moderate amounts compared to the primary essential nutrients like nitrogen, phosphorus and potassium. Magnesium in plants plays an essential role in photosynthesis, that process that plants use to make energy for growth.

[00:02:53] Also protein synthesis which is necessary for cell formation. Activation of plant enzymes needed for many cellular and growth functions and chlorophyll synthesis that green pigment in plants that is essential for optimum plant growth. Sulfur is used in our plants also for the development of chlorophyll which

[00:03:12] improves photosynthesis and the growth rates, increased resistance to pests and diseases and helps produce necessary enzymes and plant proteins within the plant. In fact some plants like mustard, onion, garlic and broccoli need adequate sulfur to produce their flavors.

[00:03:34] Now if you want a refresher on macro, secondary and micro or trace nutrients I will link to episodes in the show notes where we talked all about those plant nutrients in depth. So if magnesium helps increase intake of phosphorus which is great for flowering and fruiting

[00:03:53] and it boosts production of chlorophyll giving a healthy green color to the plant leaves and encouraging absorption of CO2 then using epsom salts on our plants should be a good thing, right? A lack of magnesium can contribute to an overall anemic appearance in your

[00:04:12] plants. In fact magnesium deficiency is first seen as intervainal chlorosis so that is the yellowing of the leaf tissue that is between the veins of the older leaves. Usually when gardeners are talking about epsom salts they're talking about tomato plants so we'll just use that as an example.

[00:04:29] When tomato production or with tomato production it is widely known that calcium levels in the soil are important for prevention of blossom and rot. That ugly little scarring that happens or rotting that happens on the bottom of the fruit at the blossom point

[00:04:48] that makes the fruit pretty much inedible. So tomato gardeners have always focused on making sure there is enough soil calcium or maybe too much calcium in the soil sometimes to prevent this from happening. Another nutrient, another one of the primary nutrients potassium is also important for

[00:05:09] plant and fruit quality and for regulating water movement within the plant plus a whole bunch of other really important functions. Now even though blossom and rot resulting from calcium deficiency can cause those tomato fruits to be inedible if we have a magnesium deficiency

[00:05:29] it can reduce the overall plant health and ultimately you are going to have lower quality fruits and you're gonna have fewer of them. And then if we have low potassium in the plant that can make the plant less tolerant of heat

[00:05:44] and drought stress which obviously we're growing tomatoes in the hot the heat of the summer so we want it to have those qualities. But here's the kicker. Calcium and potassium and magnesium compete with each other for being taken up into the plant

[00:06:03] and whichever one is more abundant in the soil is actually going to be taken up by the plant more readily than the other two which means that you can end up with an imbalance or even worse a downright deficiency in the plant even if there are adequate levels

[00:06:22] of all of those nutrients in your soil. I mean who knew plant nutrients were so fussy right? So if someone says to use epsom salts on your tomato plant because you've got blossom and rot well take note an over abundance of magnesium can actually harm your soil

[00:06:42] and hinder your plants and since magnesium actually hinders calcium uptake not only would it not prevent the blossom and rot it could actually cause it. Calcium can be notoriously slow to move so the more magnesium you have the less likely the plant is going to get enough calcium.

[00:07:00] Now secondarily to this if you have too much magnesium in your soil and it's not taken up in the plant it has to go somewhere so either it's gonna leech into the ground water and end up elsewhere in

[00:07:11] your garden or your yard or it's gonna settle into the water table and eventually end up in a river or a stream and that can upset you know the ecosystem so then this goes for any

[00:07:20] mineral or nutrient that is applied in excess in our gardens so just be mindful of that when you're adding anything to your garden or to your yard make sure that there is a need for whatever it is that you're applying. So if you see

[00:07:35] signs of a magnesium deficiency in your plants like those yellowing leaves with the intravenous chlorosis we talked about then yes you can use epsom salts to help correct that problem. But the best way to do this

[00:07:50] is by creating a foliar spray of about 2% epsom salts to water so maybe one or two tablespoons per gallon of water and not by applying it to the soil. So by doing it as a foliar spray you're going to prevent the magnesium from building

[00:08:05] up in the soil and interrupting the uptake of the calcium or the potassium. This is also a good solution if you see signs that your plants are low in phosphorus even though your soil test shows that you have plenty of it in the soil.

[00:08:19] Remember magnesium helps with phosphorus absorption so if you're seeing stunted growth delayed maturity poor root development small leaves or just sort of random defoliation and your soil test looks good then try an epsom salt spray. Don't just use it because you want to see more lush

[00:08:40] growth though more isn't always better. Using it without cause can result in too much leafy growth and unless you're growing something specifically for its leaves like lettuce or kale or something like that too much leafy growth can take resources away from

[00:08:57] fruit production so use the epsom salt spray judiciously just like anything else. See the signs react accordingly don't just spray and hope it works because you might cause more harm than good. So that's the magnesium in epsom salts what about the sulfur

[00:09:16] remember chemically epsom salt is hydrated magnesium sulfate so it's about 10% magnesium and about 13% sulfur sulfur is a key element in plant growth it is critical to the production of vitamins and amino acids and therefore protein and enzymes it is also the compound

[00:09:37] that gives vegetables like broccoli and onions and garlic their flavors. Now sulfur is very seldomly deficient in most garden soils here in North America because it gets it from the rain it's used in or it gets it from the commonly used animal manures that we use

[00:09:57] in compost those all contain sulfur and if you're using any kind of a chemical fertilizer like ammonium sulfate there is plenty of it in there so we're not usually deficient in the soils of course that doesn't always mean that our plants are taking up

[00:10:13] that sulfur in adequate amounts so it's good to know what a sulfur deficiency looks like because there can be situations that prevent the plant from taking up the sulfur. So if you have pale green yellowish green or completely yellow leaves similar to a nitrogen deficiency but you're

[00:10:32] going to see it in the younger leaves first those top leaves not the older ones you might see stunted growth reduced yields smaller than usual leaves that have like a bronze or a purple tint to them and then they do this sort of leaf cupping on

[00:10:49] the new leaves that there is a sulfur deficiency so if you see sulfur deficiency again a foliar spray is going to be most effective here for quick absorption or you could water the plant with one or two tablespoons of Epsom salt in a

[00:11:05] gallon of water provided that you are not worried about it interrupting the calcium uptake. Now what about the claim that Epsom salts help with seed germination? Okay, the best way to explain this is how one of my plant professors described a seed and I have always used

[00:11:26] this terminology ever since a seed is a baby plant in a box with a sack lunch. Okay, in other words the plant that will sprout from that seed has everything it needs inside the seed casing to feed itself while it sprouts. Most seeds

[00:11:45] don't need any external nutrients in order to germinate. In fact, most seeds contain enough essential minerals to initiate both root and shoot growth just by being placed in a moist paper towel. That being said magnesium is one of those nutrients that is essential for seed sprouting. So it

[00:12:04] stands to reason that once the seed coating is penetrated by the water in the soil, then an extra boost of magnesium would help that seedlings sprout out of the soil faster. If you've had difficulty getting seeds to sprout with strong growth in

[00:12:22] your indoor seed starting setup which is likely caused by soil conditions like incorrect temperature or moisture, then the addition of epsom salts to the seed starting mixture may give them a boost. But if you've successfully sprouted seeds without any help in the past, then there is absolutely no

[00:12:41] reason to start using epsom salts now. That's the science stuff right? Epsom salts may be helpful on plants that are grown in soils that are slightly deficient in magnesium, maybe the more alkaline soils because that high pH could actually slow the movement of

[00:13:01] certain nutrients. Or if you have very acidic like low pH soils where there's going to be a natural magnesium deficiency, and then maybe soils that are naturally high in calcium and potassium where the magnesium just can't compete for uptake into

[00:13:16] the plant. Gardeners in informal ad hoc studies who have tested using an epsom salt spray in peppers and tomatoes and roses often swear that the leaves are more lush which I totally believe and that the fruits were bigger than without

[00:13:35] the epsom salts. But there are very few controlled studies with the exception of onions that have been able to definitively show the direct benefits of using epsom salts and oftentimes has actually been shown to be detrimental to plant growth. Why? Well, because of all the other

[00:13:56] variables in the soil such as the pH and the calcium and potassium content and the weather and anything else that may affect plant growth. They've even tested in hydroponic situations where everything was carefully controlled and been unable to reproduce favorable results consistently where the

[00:14:16] epsom salts were proven to be the catalyst. And for the onions, well my best bet is the improvement was due to the sulfur in the epsom salts. So just like anything in the garden, whether or not it works will depend on your garden,

[00:14:29] your soil, your weather, your crop. Just use any home remedy sparingly and only when you see signs that your plants need it. Until next time my gardening friends keep on cultivating that dream garden and we'll talk again soon. Thanks for

[00:14:44] listening to another episode of Just Grow Something Podcast. For more information about today's topic and to find all the ways you can get in touch with me or support the show, go to justgrowsomethingpodcast.com. Until next time my gardening friends keep learning and keep growing.