Epsom salt can be harmful

Q. What is happening to my tomatoes? They start out nice, but then the bottom turns black and decays.

Elizabeth from Canfield

A. The problem is blossom end rot.

This is not a disease.

The problem is caused by a lack of sufficient calcium in the plant’s vascular system. Soil pH can be the problem here, but most likely not.

Calcium uptake by the tomato plant is affected by moisture levels. Plants in the ground should have plenty of water this season, and thus, not as many problems with blossom end rot.

Tomato plants in greenhouses, hoop houses and planted in pots are a different story. These plants are watered using garden hoses, soaker hoses and other means of irrigation.

Tomato plants need 1” of water per week as they are growing.

When they have fruit on them, they need upwards of 2” of water per week.

If the plant gets dry for a few days with no water or not enough, the plant reduces the uptake of calcium from the soil and the lack of sufficient water can affect the movement of calcium within the plant.

The result is too little calcium for cell walls and thus a breakdown of the plant tissue, resulting in a dark spot on the bottom of the fruit.

This fruit can still be eaten and canned, just cut off the bad part.

Be sure this is indeed the problem before canning.

The other issue with blossom end rot seems to be Epsom salt.

Many people tell me it’s great to put it on tomatoes during the growing season to “make better tomatoes.”

But it’s no magic bullet.

The chemical in it is magnesium sulfate, a highly soluble form of magnesium which does not affect soil pH.

The reason people use it is due to low magnesium levels in the soil.

But if you have not tested the soil you do not know if your magnesium level is high or low.

Most of the time it is not necessary and there are better options.

The misuse of Epsom salt can be a problem when it is not needed.

Some plants are quite sensitive to magnesium toxicity; it can kill them.

Also, the magnesium in Epsom salt can replace calcium in soil, thus causing calcium deficiency and explaining why I get lots of calls about blossom end rot on tomatoes from people who use Epsom salts.

Eric Barrett is OSU Ext. educator for agriculture and natural resources in Mahoning County. Call the office hotline at 330-533-5538 from 9 a.m. to noon Mondays and Thursdays to submit your questions.

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