Bottom rot help!

They probably need to be elevated off the ground some. That's why I use tomato cages to keep them up. I also put dried grass, or straw, mulch under the plants. When I used to let the tomato plants just grow and lay on the ground, most of them would develop black spots on the part of the tomato that was touching the ground. Not positive, but I think it's the constant dampness of the ground maybe. It's not too late in the season to gently stick some mulching around the plants where the plants touches the ground. I have lots of volunteers too that come up from last years tomatoes. It's a nature freebie that I love to find!

I was going to say besides what the other posters had mentioned was to maybe only water in the morning or by base/roots of the plant. I've been told if you water in the evenings it can promote rot as the water doesn't absorb very will and can cause problems. Usually my only problems in this regard were a bad variety of tomato. One year I had bought some that were on sale at a gardening chain store and as soon as they started being the right shade of red they'd start forming a dimple in the skin and start rotting on the vine. I know it wasn't just me because my Aunt had bought the very same plants and had the same thing happen. So perhaps if you buy your plants already started to look elsewhere. We bought an heirloom by mistake one year an it was huge atleast 2lb fruit. Only problem was by the time it was almost ready to pick it would start to spoil. We tried to pick them early and let them ripen in a bag and that only worked part of the time. I was very disappointed.

Firstly, let me say, I am totally envious...this has been the worst year in my area for tomatoes, or anything of the cucurbit family. Nights are so cold! Heartily agree that mulching will help, and also prevents infection from any soil born diseases like fusurium or fusillium wilt, as it keeps the spores from splashing up onto the plant (creating infection) when watering. As far as I know, despite the unappealing appearance, this common tomato malady is NOT caused by a disease organism...but by water stress. It happens when the plant is suddenly exposed to hot dry weather or water deficiency! Water stress causes the plants leaves, in dire need of water to draw it from the far ends of some of the fruits. The fruit cells, now deprived of water, will shrivel up and form the black area. Often, too, the soil is lacking in sufficient calcium. Hoping you have a tremendous harvest. Cheers!