(image from the Ohio State University Extension website)
I have been growing a small crop of tomatoes for the last number of years, and every year I have had great success and fruit production. I grow my tomatoes in the same spot every year and I know it is good to rotate them, but unfortunately my small garden does not allow me that freedom. This year I noticed a new problem and I am not sure what to do about it. As the tomatoes begin to turn red the bottom of the fruit begins to turn black and soft. I have done some research and I think the problem is called Blossom End Rot. Can you help me confirm the problem and how best to fix it?
I am really glad you called with this question because the exact same happened to me in a small garden I planted last year. The tomatoes would develop these decaying spots that were brown or black, usually at the base, or “blossom end”, of the fruit. Even though Blossom End Rot sounds like a disease, it is actually more of a cultural condition taking place between the plant and the soil it is grown in.
Sure enough, your condition is Blossom End Rot, and the reason for it is a lack of calcium in the soil. Calcium is important in plants because it facilitates water uptake and strong cell development and division. Calcium deficiencies in your tomato plants can be because it is simply lacking in the soil, but your watering schedule can have an affect as well. Tomatoes require their roots to be evenly moist through the growing season and when very wet soil is followed by very dry conditions the calcium distribution to the plant can be compromised. This year especially our rainstorms have dropped so much water in such a short time, followed by long dry spells in between, and our plants have suffered from the irregular watering. Therefore, make sure your tomatoes are well watered during the dry spells. In addition, do not be afraid to mulch your plants because that helps regulate soil temperature and moisture levels throughout the growing season.
To fix this problem I have yet to discover a “quick solution”. What I can tell you is that there are a number of long term amendments you can make to your soil so that your tomatoes next year come back with the same fervor and success you are used to. If you do not add it already, compost should be on the top of your list. Not only does compost increase water permeability and drainage, add organics and micronutrients to the soil, and improve soil structure, but it also helps regulate soil pH. Secondly, you need to add calcium back into the soil. Ground limestone can be applied once in the fall and it will slowly release calcium into the soil to help you prepare for next year’s planting. Even though they may sound like applicable products for the task, a few reference books I used here in the library said to stay away from quick lime and hydrated lime. If you cannot find limestone, then adding Gypsum to the soil will also help increase the calcium levels in the soil. If you are determined to take a much more “au natural” approach, I can tell you what we used to do in my mothers garden growing up on Long Island. Because the soil is naturally so acidic, we would get oyster and clam shells from the local seafood shop, pulverize them, and add the dust to the soil along with compost in the fall. As I say, I am sorry none of these are such quick fixes, but at least now you have a little more knowledge of soil science and know how to prepare your soil for your tomato crop next year.