Guess what? I am not the world's best gardener. Even your hardworking Garden Manager sometimes fails to take proactive measures to protect the fruits of my considerable labor. And even though I generally try to be Rebecca of Sunnybrook Farm on this site, this article relates the dirty secret of my tomato crop this year: Blossom End Rot (the notorious BER which surfaces just as you've gotten excited about harvesting the pefect red fruit). I've been asked about it before by friends, family and SACG Gardener for years, but have never suffered from it myself except when growing roma tomatoes in clay pots on the south side of my house. This year, I've noticed BER on quite a few of my plants at the SACG and at home and so feel the need to share my pain with the world.
As most of you know, BER is caused by calcium deficiency. By the time you see the tell-tale black spots on the bottom of your tomatoes, however, it is too late to save them by throwing egg shells or bone meal at the plant roots. Foliar sprays I am reliably informed will not help, either. You can only work to improve the conditions going forward (generally next year). On the positive side, it is not a virus and is not contagious. Just because your determinate tomatoes may be lost, does not mean that it will spread to your indeterminate tomatoes if you timely address the adverse conditions.
It is important to note that you cannot always blame your compost for not containing enough egg shells. Sometimes, the plants cannot take up calcium because the pH is too high. After doing some research, I found the explanation for my problem this year on the Gardener's Supply Company website. Does this sound familiar to you?
Blossom-end rot is most common when the growing season starts out wet and then
becomes dry when fruit is setting. Damage first appears when fruits are approximately half their full size. The water-soaked areas enlarge and turn dark
brown and leathery. These areas will eventually begin to rot, so the fruit should be picked and discarded. Several factors can limit a plant's ability to absorb enough calcium for proper development. These include: fluctuations in soil moisture (too wet or too dry), an excess of nitrogen in the soil, root damage due to cultivation, soil pH that's either too high or too low, cold soil and soil high in salts.
The only way to avoid BER is to take steps before it appears. Add Epsom salts or bone meal to the soil when planting and avoid adding excess nitrogen or excess moisture. Aim for soil pH of 6.5 (which means not adding lime where your pH is above this level like it is at the SACG). Control moisture fluctuations with mulch (like straw).
At the SACG, we have a sufficient amount of calcium in our soil, but not in surplus amounts. We also have an abundance of nitrogen and most of us mulch our tomato plants with straw. However, like everyone else, we had a freakish amount of rain in the early growing season and then the rain stopped unexpectedly in July while the tomatoes were setting fruit. These are the classic conditions for BER. I water my tomatoes generously once or twice each week. However, with our extreme heat this month, I apparently was not watering all of my plants enough. Sigh.
Ohio State's Extension's site has the ultimate scientific article about BER, if you want to read something with a little more gravitas that I ever impart here.
In the meantime, if you find BER on your tomatoes, be prepared to toss them (somewhere other than the compost pile if you want to avoid volunteer tomatoes next year). I generally toss tomatoes as soon as I see BER on green tomatoes so that the plant can put its energy into ripening and enlarging the good tomatoes left on the plant. However, I'm not proud. I often just cut out the spot (even if it has ruined the bottom half of the tomato) and eat the rest. The good half of the tomato is quite edible. I'm crossing my fingers that I have some tomatoes to harvest tomorrow because I would like to start canning sometime this summer . . . .