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. You can use these natural products specifically developed to treat, prevent, and slow blossom end rot in tomatoes: Enz-Rot Blossom End Rot (a concentrate that can make up to 8 gallons) and Tomato Rot-Stopicon (in a ready-to-use spray bottle.) Follow package directions for application. Or 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.
  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

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

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Oct 13, 2015
Rot on "tops" of tomatoes " after they were picked"
by: Cathy Chandler

The "bottom" of my tomatoes are great! It is the tops that rot!

Jul 16, 2015
Black spots on tomatoes
by: Anonymous

My tomato fruit are still very green but I am noticing the large black spots appearing on the sides of the fruit.

Jun 11, 2013
by: Russ

I don't have a solution, but I have battled BER before that is not BER. BER tends to come before the tomato is set and can cause the tomato to rippen prematurely. If this persons problem is the same as mine the tomato is set and has begun to rippen and then almost overnight the rotten spots come. Not on the bottom but on the side and top.

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