Black soft bottoms on red tomatoes

by Lee Y.
(Chicago, IL)

Dear Tomato Dirt,
I have potted 2 tomato plants and they look great. They're growing well with green leaves and tons of tomatoes and flowers. However, as they turn red, the bottoms are black and soft. I have an extremely well-drained pot. I water until the water comes out the bottom. I don't know what this is or what to do.

Sincerely,
Lee Y.

Dear Lee,

Sounds like your tomatoes have blossom end rot, which is a tomato problem that's most common in early to mid-season. It's caused by a calcium deficiency. The tomato's cells need calcium in order to grow in a healthy way. Plants get calcium from watering. But calcium moves slowly. So when calcium doesn't get to the tomato's extremities (the bottom of the fruit), then cells wither and die.

So ... since you've been watering consistently, sounds as if there's something else impeding the calcium uptake. Other conditions can inhibit calcium absorption, such as excessive temperatures (either hot or cold), root damage, too much nitrogen in the soil, or even a pH imbalance.

First thing to check: have you been feeding plants with a balanced tomato fertilizer? Since you water faithfully, nutrients will leach out of container. Tomatoes in pots need to be fertilized every 7-14 days. Make sure you've got plants on a good feeding schedule.

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.

Some gardeners report success treating blossom end rot quickly by spraying tomato plants with milk 2-3 times a week, which is high in calcium.

You didn't say what kind of medium you used for planting, but it's always a good idea to use a sterile potting mix in containers. You'll remove many of the pH and other chemical imbalance issues.

Make sure plants are protected in the early part of the season, especially if temperatures are cool.

With proper feeding and watering, blossom end rot usually clears up quickly in tomato plants.

Good luck - and we look forward to hearing that those nasty black spots clear up.

Happy Gardening!
Tomato Dirt