Blossom End Rot on Tomatoes

by Shirley
(Ordway, CO)

Q. Some of my tomatoes have a black spot on the blossom end (not stem end). Can you tell me the cause and cure for this problem?

A. Blossom end rot (BER) is caused by a calcium imbalance. Tomatoes need calcium to grow - it acts like glue in tomato tissues, binding them together. When tomato plants are under stress, they have difficulty with calcium uptake, because calcium moves slowly. Tissues break down. That causes the rotted, leathery ends on your tomatoes.

Excessive heat is one stress factor that causes BER. It's likely that current high temperatures may be stressing your plants. Root damage, inconsistent watering, too much nitrogen, salt, alkaline or acid soils - these are all culprits in the BER debate.

BER is often most prevalent during early to mid-season.

As far as what to do about it, prevention is the best treatment. (Learn more about preventing blossom end rot.)

BER is irreversible in affected tomatoes, but you can keep additional fruit from acquiring it. Treat immediately with calcium. Mix 1 tablespoon calcium chloride (sold commercially for other uses as de-icing salt or DampRid® Closet Freshener) in one gallon of water. Spray 2-3 times a week until blossom end rot is under control. Or alternatively, spray with milk. Further, pick affected fruit to reduce stress to the plant. Make sure you keep your plants on a regular watering and fertilization schedule.

Fortunately, blossom end rot needn't last all season. You still can get plenty of healthy tomatoes before frost!

Good Luck and Happy Gardening!
Your friends at Tomato Dirt