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Will Epsom Salt Kill Grass? Not Really — and That's the Problem

Epsom salt is magnesium sulfate, not a herbicide. It won't reliably kill grass, and the vinegar-and-Epsom recipes work through the vinegar.

By Zakaria 3 min read Save to Pinterest — opens Pinterest in a new tab
Close-cut lawn with a straw-coloured patch of dead grass running across one corner of otherwise green turf
Photo: Saúl Ticona, Pexels License, via Pexels
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No — and the reason matters. Epsom salt is magnesium sulfate, a plant nutrient. It is chemically unrelated to table salt, and “salt kills plants” comes from sodium chloride, which works by an entirely different mechanism.

The name is doing all the damage

Two completely different compounds
Epsom saltTable salt
CompoundMagnesium sulfateSodium chloride
Role for plantsA nutrientToxic in quantity
How it harmsOsmotic scorch, only in excessDisrupts water uptake; persists in soil
Kills grass?UnreliablyYes, and sterilises the ground

They share the word “salt” and nothing else that matters here.

Why the famous recipe works anyway

The vinegar is doing the work; the Epsom salt is along for the ride

In the standard vinegar + Epsom salt + dish soap mix:

  • Acetic acid in the vinegar destroys cell membranes on contact — this is the herbicide
  • Dish soap is a surfactant that helps it stick to waxy leaves
  • Epsom salt contributes very little. Tested against vinegar and soap alone, it makes almost no measurable difference

The recipe works. People credit the wrong ingredient.

And it does not kill grass permanently

Household vinegar at 5% acetic acid does not travel to the roots. What you get:

  • Everything green burns off within hours — dramatic and convincing
  • Perennial grasses and deep-rooted weeds regrow in one to three weeks from the crown, often looking worse

It is a contact burn-down for annual weeds in paving, not a way to clear a lawn.

Is it bad for your lawn?

In small amounts, harmless. Routinely, pointless:

  • Magnesium deficiency is uncommon in most soils — you are usually adding what the grass already has
  • Excess magnesium interferes with calcium and potassium uptake
  • The sulfate acidifies soil over time

Without a soil test, you are guessing.

If you have a dog, the mulch question is worth checking too — is cedar mulch safe for dogs.

What actually kills grass to the root

Methods that reach the roots
MethodTimeNotes
Sheet mulching2–3 monthsCardboard + mulch. No chemicals
SolarisationHottest 6–8 weeksClear plastic, full sun
Systemic herbicideDays to weeksWhere permitted and appropriate
Boiling waterImmediate, repeatBest for paving cracks

For weeds between paving, a kettle of boiling water does the job better, faster and for nothing.

Common questions

Will Epsom salt kill grass?

Not reliably, and not in the way the name suggests. Epsom salt is magnesium sulfate, which is a plant nutrient rather than a herbicide — it is chemically unrelated to table salt, and the salt-kills-plants association comes from sodium chloride, which works by disrupting water uptake. Applied heavily enough Epsom salt can scorch foliage and cause an osmotic effect, but it is an unreliable, expensive and slow way to kill grass.

Why do weed killer recipes include Epsom salt then?

Because the recipe works and people credit the wrong ingredient. The standard vinegar, Epsom salt and dish soap mix kills top growth through the acetic acid in the vinegar, which destroys cell membranes on contact. The soap is a surfactant that helps the mix stick to waxy leaves, and the Epsom salt contributes very little. Tested against vinegar and soap alone, adding Epsom salt makes almost no measurable difference.

Does that vinegar mix actually kill grass permanently?

No. It burns off everything green it touches within hours, which looks dramatic and convincing, but household vinegar at 5 percent acetic acid does not travel to the roots. Perennial grasses and deep-rooted weeds regrow within one to three weeks from the crown, often looking worse than before. It is a contact burn-down for annual weeds in paving, not a way to clear a lawn.

Is Epsom salt bad for a lawn?

In small amounts it is harmless and occasionally useful, but routinely applying it to a lawn without a soil test is pointless at best. Magnesium deficiency is genuinely uncommon in most soils, so you are usually adding a nutrient the grass already has enough of. Over-applying magnesium can interfere with calcium and potassium uptake, and the sulfate contributes to acidifying soil over time.

What actually kills grass permanently?

For clearing an area, sheet mulching or solarisation kill grass completely without chemicals — cardboard and mulch over the area for two to three months, or clear plastic through the hottest part of summer. Both kill roots as well as top growth, which is the part household recipes miss. A systemic glyphosate-based herbicide also kills to the root where its use is permitted and appropriate, and repeated close cutting plus smothering works given time.

Does Epsom salt kill weeds in paving cracks?

Boiling water does the job better, faster and for nothing. For weeds in paving, pouring a kettle of boiling water on them kills top growth and much of the shallow root immediately, and repeating it every few weeks exhausts the plant. If you prefer a spray, use horticultural vinegar at a higher concentration than kitchen vinegar, with appropriate care — the Epsom salt in the recipe is not doing the work.

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