Big black/brown areas on the bottom of unripened tomatoes. What are they?

by Kathy Shelton
(Reidsville, NC)

Q.Our tomato plants are all at the early stages of the small green unripe tomatoes but on the bottom of the tomatoes that are maturing is a black/brown area. What is causing this and how can we prevent it so we don't loose any more tomatoes?

A. It sounds like blossom end rot (BER). Most gardeners notice it in on affected tomatoes when the first fruit is about 1/3 to 1/2 its full size.

It's caused by a calcium imbalance. That may or may not mean your soil has enough calcium. What the real problem is, however, is that the tomato plant is struggling with calcium uptake.

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.

Tomatoes are particularly susceptible to blossom end rot when they're under stress - too hot, too cold, too dry, too wet, too much nitrogen in the fertilizer ...

Bottom line, our tomatoes like consistency.

As for now, 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.

Pick the affected fruit. You can cut out dark areas and eat the remainder.

Most tomato plants that suffer from BER early in the season recover well as the summer progresses, especially if you give plants a consistent amount of water (1-2 inches a week.)

You can read more about blossom end rot on its very own page!

Good luck and happy gardening!
Your friends at Tomato Dirt