Epsom salts as a garden cure-all

The claim

Epsom salts added to soil or sprayed on leaves boost growth, green up foliage, sweeten tomatoes and prevent blossom-end rot.

What the evidence actually shows

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 fertiliser claim.

The one legitimate use

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 to do 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.