Don’t let blossom end rot ruin your vegetables

Blossom end rot can develop in tomatoes, but occasionally in peppers, eggplant and squash. Learn how to prevent this physiological problem from ruining your garden vegetables.

July 2, 2014 - Author: Gretchen Voyle,

Blossom end rot symptoms on tomatoes. Photo credit: David B. Langston, University of Georgia,
Blossom end rot symptoms on tomatoes. Photo credit: David B. Langston, University of Georgia,

Tomato growers of the land, rejoice! There is a way of preventing a tomato problem called blossom end rot. For many gardeners, those tomatoes that have flat, black or brown bottoms are so discouraging. What caused their tomato to only make half of a fruit? There are several explanations for what is described as a physiological problem – this means it was not insect- or disease-related.

Michigan State University Extension horticulture educators and Master Gardener hotline staff will begin receiving their first phone calls as those first tomatoes ripen at the end of July. The callers are suspecting that some foul tomato disease is afoot, but the answer is simpler. Blossom end rot has to do with water. Tomatoes producing fruit need regular, deep watering when there is no rain. Technically, blossom end rot is caused by a calcium deficiency, but the real reason is that there is not enough available water in the plant to transport that calcium into the fruit. The water acts as the transporter. Most Michigan soils have abundant natural calcium. The calcium is there in the soil, just waiting for a ride, but the problem develops when watering plants is not deep enough.

Tomato leaves are soft in comparison to the fruit. As the sun shines on the leaves, moisture evaporates out of the leaves in a process called transpiration. Transpiration cools the leaves, but is also the “pump” to cause water to be pulled into the leaves. However, the tomato fruit is like patent leather shoes: it’s tough and shiny and very little transpiration takes place there. When there is not enough water, the tomato leaves successfully pull the moisture into them. Hot weather may make problems worse. The gardener is watering the same, but the demands have gone up.

Smart gardeners realize that a simple, inexpensive rain gauge is their best ally in the water wars. This records the amount of precipitation that has fallen. The goal would be for the garden to receive a minimum of 1 inch of water per week in 1 square inch of soil surface. A smart gardener keeps track of rainfall and supplies what is missing. In the case of tomatoes, it is critical for the production of those beautiful red orbs.

Other possible reasons for blossom end rot could be that the tomato plant makes a mistake with its first fruits as it adjusts to the big demands of making fruit and then it self-corrects. It can also happen when the plant has not developed a big enough root system to take in enough water. This is seen often with tomatoes planted in containers that are too small. For many of these containers, it has to do with the width, not the depth, of the pot. Roots grow horizontally and when they reach the sides of the container, they grow downwards and are crowded. For plants in containers, choose tomatoes that are labeled as “patio tomatoes.” They do not grow larger all season, but grow to a certain size and produce their fruit then. Choose containers for width in mind.

Another possibility is that the soil is deficient in nutrients and a big root system did not develop. That can be solved with a soil test. Visit for more information on soil testing and to purchase one.

Other garden vegetables such as peppers, eggplant and squash can also have blossom end rot, but it is not as likely. Not enough water will cause the fruit to suffer first. In your home garden, keep track of rainfall and check the moisture in the top 2 inches of soil. When the soil is dry, replace it. Water should be placed all the way around the plant. Keep in mind that a large tomato plant’s roots could be 1 to 3 feet away from the stem.

Nothing beats the sweet tanginess of those perfect red tomatoes from your garden. Don’t let blossom end rot ruin the party.

Tags: community gardening, home gardening, lawn & garden, msu extension, pest management, vegetable gardening

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