Does Epsom salt help tomatoes and plants?
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Only when a soil test shows magnesium deficiency. Plants need magnesium in minimal quantities, and garden soil amended with organic matter usually has enough, so adding more does not improve growth. Excess magnesium sulfate accumulates in the root zone, impedes water uptake and inhibits calcium uptake, which can make blossom-end rot worse rather than better.
What do people believe about Epsom salt?
Epsom salts added to soil or sprayed on leaves boost growth, green up foliage, sweeten tomatoes and prevent blossom-end rot.
What does the evidence show?
Clemson Cooperative Extension addresses this directly. Magnesium is required only in minimal quantities and is generally already sufficient in garden soil amended with organic matter. Applying more does not improve growth in a soil that is not deficient.
The blossom-end rot claim is worse than merely ineffective. Excess magnesium sulfate is a salt: it accumulates in the root zone, impedes water uptake, and inhibits calcium uptake. Since blossom-end rot is a calcium-transport disorder, adding a competing cation can make it worse. The remedy actively works against the condition it is sold for.
The University of Minnesota Extension review reaches the same conclusion on the general fertilizer claim.
What is the one legitimate use of Epsom salt?
A soil test showing magnesium deficiency. That is a real condition, it does occur in some sandy and heavily leached soils, and magnesium sulfate is a perfectly good way to correct it. The problem is applying it without knowing, on the assumption that more of a nutrient must be better.
What works instead?
Soil test first. For blossom-end rot, address the actual cause - irregular watering, root damage and rapid growth swings that disrupt calcium transport - rather than adding calcium or magnesium to a soil that has plenty of both.
Key takeaways
- Plants need magnesium only in minimal quantities.
- Garden soil amended with organic matter usually holds enough magnesium already.
- Excess magnesium sulfate impedes water uptake and inhibits calcium uptake.
- Blossom-end rot is a calcium-transport disorder, so extra magnesium can worsen it.
- Magnesium deficiency does occur in some sandy and heavily leached soils; test first.
References
Frequently asked questions
When does magnesium actually help?
When a soil test shows magnesium deficiency. That is a real condition in some sandy and heavily leached soils, and magnesium sulfate is a perfectly good way to correct it.
Does Epsom salt prevent blossom end rot?
No, and it can make it worse. Excess magnesium sulfate inhibits calcium uptake, and blossom-end rot is a calcium-transport disorder. Address the actual causes instead: irregular watering, root damage and rapid growth swings.
Does Epsom salt boost plant growth?
Not in soil that is not deficient. Clemson Cooperative Extension and University of Minnesota Extension both conclude that applying more magnesium does not improve growth where soil already has enough, as most garden soil amended with organic matter does.
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