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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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Aug 31, 2017
Tomato issues.
by: Nico

We do about 40 - 50 plants per season. This year we found that the tops were rotting away, almost like it was burnt but still green while the rest was ripe and tasty. Can this be something from above? Chemical trails from planes? First time seeing this in our garden in 38 years at this residence. We use our heirloom seeds from over 50 years ago, never had this happen. Thought it could have been some calcium that was added to the soil but now its happening in the smaller garden where no calcium was added. Now I'm thinking its something airborne as we don't live to far from an airport.

Jul 10, 2017
Rotten spots on ripening tomatoes
by: Angie

That is exactly what mine are doing too, Russ. Any solutions?

Jul 23, 2016
The black spots on the tops of the tomatoes
by: Ann

That is NOT blossom end rot. I'm having the same issue with one particular breed. We planted 5 breeds this year. That is a fungal infection. Blossom end rot is on the bottom of the tomato. We have a different breed with blossom end rot. Looks nothing like this.

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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