The symptoms of blossom-end rot on tomatoes start off as a small, tan-colored spot on the blossom-end of a tomato fruit. If you’re an obsessive tomato grower that is constantly examining your fruits, you’ll noticed it first when the fruit is small, green, and still developing.
Depending on the size and shape of your tomato you may not notice it until the fruit is ripening and the problem worsens and develops into a dry, leathery lesion that is hard to miss.
Blossom-end rot isn't a disease spread by garden pests, or something that is transmitted through infected plants. It also isn’t a result of a poorly pollinated flower. Generally blossom-end rot occurs when a developing tomato fruit doesn't get the necessary amount of calcium to the end of the fruit while it starts to develop.
Preventing Blossom-end Rot
This disordered is primarily caused by uneven watering when the fruits are developing that doesn't let the tomato plant take advantage of nutrients in the soil-especially when you’re growing tomatoes in containers. Extended droughts, over watering, or drought followed by over watering can lead to blossom-end rot. Basically, your tomatoes are getting blossom-end rot because you’re not watering properly when the plant needs it most. Don’t let your tomatoes sit in soggy soil and don’t let the soil dry out to the point that the plant is wilting.
Tomatoes Affected by Blossom-end Rot
A couple of years ago while talking to Colleen from In the Garden Online I learned that the elongated, paste-type tomatoes are highly susceptible to blossom-end rot. She pointed me to the paper A Cellular Hypothesis for the Induction of Blossom-End Rot in Tomato Fruit which puts the blame on blossom-end rot in elongated tomatoes on the shape and vascular structure of the fruit. Basically if you’re growing paste tomatoes you’re going to have to live with blossom-end rot occurring.
If your tomatoes are showing signs of blossom-end rot you can just simply remove the affected fruit(s) and ensure you properly water your tomatoes from here on out to keep the rest of the crop from being affected.
Blossom-end rot also affects vegetables like peppers and eggplants, and the solution when it happens with those vegetables is the same.