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Master gardener: How to protect tomatoes from blossom-end rot

By in Press Enterprise on July 14, 2017

By Ottillia "Toots" Bier

Question: Do you know what is wrong with my Roma tomatoes? Do they have a disease? What should I do?

Answer: I believe your tomatoes have blossom-end rot, a physiological disorder, not a disease. Tomatoes afflicted with blossom-end rot have blackish, dark brown or tan dry areas at the blossom end of the fruit. Some tomato varieties are more likely than others to develop this condition. Roma tomatoes are especially susceptible, salad and beefsteak tomatoes are moderately susceptible, and cherry tomatoes hardly ever develop it.

Blossom-end rot occurs when the developing fruits experience a shortage of calcium, a necessary nutrient for all plants. When a tomato plant is very actively growing, water and calcium demands are high, and the plant’s roots take up the needed water and calcium, as well as other nutrients, and deliver it preferentially to the leaves. This may leave the developing fruits with less calcium than they need for proper development. Consequently, the fruit cells break down, leading to blossom-end rot.

Most California soils are not deficient in calcium, but if yours is, amending the soil with calcium may help prevent the problem. You can add a handful of garden lime (calcium carbonate) to the soil at planting time. Most nurseries or home improvement stores carry it in 3- to 5-pound bags. It is usually located with the fertilizers. Be sure to mix it thoroughly into the soil that will host the tomato roots. Fertilizer companies rarely include calcium in their fertilizers, and when they do, it is sometimes not enough.

Most importantly, irregular watering practices contribute to blossom-end rot problems too. Be sure your water application schedule is regular and based on the weather. Never let your plants become droughted, especially if unusually warm weather is forecast. Also, consider mulching your plants to keep the roots cooler and to […]    

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