The Q&A Archives: Calcium for Blossom End Rot

Question: Will calcium help bottom rot on tomatoes? What is a good source of calcium to use on tomatoes?

Answer: Although tomato blossom-end rot is technically caused by a calcium deficiency, surprisingly the best way to solve the problem is to keep the soil pH between about 6 and 6.8 as measured by a soil test and also to maintain a constant level of soil moisture throughout the growing season.

Soil test kits are commonly avalable at garden centers and through the County Extension. Your County Extension staff can help you with the test and interpreting the results and determining how to adjust the pH if it is necessary. Their telephone number is 560-4150. If it turns out that you do need to add a large quantity of lime, be sure to do it gradually over the coming year or so.

Blossom end rot is aggravated by either excess watering or excess nitrogen; it tends to occur when a long dry spell hits after a period when the plants have grown very fast or after a very wet rainy stretch. In other words, wide fluctuations in water availability can cause it. Try to ensure your plants receive a steady supply of moisture (if in doubt you can check the soil with your finger to see if it is moist or dry), mulch them well, and the problem should subside.

In my experience, blossom end rot looks awful but the tomatoes are still edible -- just cut away the ugly part. If you don't want to bother with tomatoes with the disorder, check the fruits when they are about one third to half sized and you will be able to see the beginning of the spots. To conserve the plant's energy you could remove them then. Good luck with your tomatoes!

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