Why are all of my tomatoes are getting big rotten spots?

by Rachel
(Shelby, Ohio, USA)

Q. The majority of the tomatoes on my 16 tomato plants are getting these large rotten spots on them before they are ripe. Does anyone know what could be causing this? Is there anything I can do to save my tomato crop this year?

A. Looks like a classic case of blossom end rot (BER). This common tomato problem appears on the bottom side of the tomato (either a green or ripened one) develops a sunken, leathery dark brown or black spot.

It's caused by a calcium imbalance. Tomatoes absorb calcium through water. But calcium isn’t fast-moving.

If a tomato grows quickly, or if other conditions slow water absorption, then calcium doesn’t have enough time to travel through the whole piece of fruit.

Plants can’t absorb enough calcium – whether or not there’s enough in the soil.

A tomato’s tissues break down and leave the telltale damage on its bottom.

Prevention is the most method of control (see below).

Blossom end rot cannot be reversed on a tomato once it’s set in, but you can take these steps to slow and halt it.

1. Preserve affected plants by applying calcium immediately. 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. Apply early in the morning when temperatures are cool. Similar ready-to-spray natural products specifically developed to treat tomatoes are sold commercially as Green Light Blossom-End Rot Spray and Bonide Rot-Stop® Tomato Blossom-End Rot Spray.
   
2. Pick affected fruit to reduce stress on the plant and allow it to direct its energy to other tomatoes.
   
3. Cut out spots on harvested fruit and eat remainder. Blossom end rot does not make the rest of the tomato inedible. However, if tomatoes have been infected by fungi or mold, discard them.
   

Learn more about how to prevent blossom end rot, when it strikes, and which tomato varieties are most susceptible to it.

Good Luck and Happy Gardening!
Your friends at Tomato Dirt