Fertilize with Epsom Salts: Epsom salts and blossom end rot

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Name: Sue
Ontario, Canada (Zone 4a)
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Jun 20, 2017 8:48 AM CST
This article states "Epsom salts can keep plants greener and bushier, enhance production of healthier fruit later in the season, and potentially help reduce blossom-end rot in magnesium-deficient soils"

Last year I applied Epsom salts (magnesium sulfate) to container tomatoes to make sure they had enough magnesium, and had the worst blossom-end rot ever.

Blossom-end rot is said to be related to calcium insufficiency. Epsom salts do not contain calcium. According to Clemson Cooperative Extension "The cause of this disorder is a calcium deficiency in the developing fruit. Extreme fluctuations in moisture, insufficient soil calcium, root pruning from nearby cultivation, and excessive ammoniacal (NH4 +) nitrogen, potassium, or magnesium fertilization can also increase the chances of blossom end rot, especially early in the season."

Note this says excessive magnesium fertilization increases the chances of blossom end rot. According to Clemson "Avoid excessive potassium or magnesium fertilization as these nutrients will compete with calcium for uptake by the plants. Epsom salts is an example of a magnesium source, so do not apply to soil unless a recent soil report indicates a magnesium deficiency" .

Clemson Extension article:

I did some searching of scientific literature via Google Scholar and could not find any reference that suggests magnesium can reduce blossom end rot as suggested in this NGA article. In fact what I found supported Clemson's contention. For example "

Hao, X. and Papadopoulos, A.P. 2003. Effects of calcium and magnesium on growth, fruit yield and quality in a fall greenhouse tomato crop grown on rockwool. Can. J. Plant Sci. 83: 903ā€“912.

"High Ca (300 mg Lā€“1) concentration increased fruit yield and reduced the incidence of blossom-end rot (BER) ............Blossom-end rot incidence increased linearly with increasing Mg concentration in the early growth stage at low Ca, but BER incidence at high Ca was not affected by Mg concentration."

I would like to see either a scientific reference provided for Epsom salts (magnesium sulfate) reducing blossom end rot or the suggestion for its use removed from the NGA article if, as it seemed to me, there is no supporting evidence. Otherwise readers may apply Epsom salts and increase their risk of blossom end rot rather than reduce it.

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