Ann,

It is Blossom End Rot, and although it is related to a calcium deficiency, that does not necessarily mean your soil is deficient in calcium. Instead, the most common cause is uneven watering that stresses plants. When plants are stressed, the calcium is pulled back into the plant from the tomatoes and that leaves them deficient in calcium which causes the BER.

I've linked a thread about BER from yesterday below. Although the original poster in that thread had other extenuating circumstances (smallish containers and a home remedy that backfired), the BER info is applicable to us all. You also can learn more about it by going to the Tomato Forum and clicking on the word FAQ at the top of that forum's main page and reading the BER section of the FAQ or you can google Blossom End Rot for all kinds of info.

Dawn

Here is a link that might be useful: Previous Discussion of BER

Thanks Dawn, That is very helpful. It happened when I was out of town and had a teenage waterer. I'll try to do better.
Ann

Ann,

To be honest, sometimes it is unavoidable, especially when our weather seesaws from "normal" to "extra hot" even if you are doing everything right. The best you can do is keep them evenly moist, mulch them to keep the soil from drying out too quickly, cross your fingers, and chant secret spells while burying a blue dishray under a stump on the night of a full moon. That's what works for me. LOL

One reason I use Espoma Tomato-Tone plant food is because it has calcium in it. My in-the-ground plants get a handful of Tomato Tone in their planting hole at planting time, and then I side dress with it about once a month thereafter. The ones in containers get it more often because of the leaching issues.

Dawn

I've had a big problem this year with my first tomatoes myself on a new section of my garden. I must say I did not do a soil test on this plot.Could be my problem calcium Too.