Question: My tomatoes are developing a black, sunken-in spot on the bottom of each of them. Other tomatoes seem to be cracking. Is there anything I can do to prevent this from happening?

Answer: What you are describing is two different plant issues with some very common causes. In both cases, you likely have issues with soil moisture fluctuations.

Tomatoes that develop a large black, leathery spot on bottom are most likely suffering from blossom end rot, which is a physiological disorder. This is especially more likely to happen in the earliest tomatoes of the season or in the driest parts of the summer. Blossom end rot is caused by a lack of calcium in the tissues of the fruit. Calcium is taken up into the tomato plant through the roots and then settles in one part of the plant. Actively growing parts of the plant such as developing tomatoes must have a continuous supply of calcium to prevent these spots from developing. The rot can occur even when there is an ample supply of calcium in the soil, stems or leaves. Calcium can only be moved through the plant with enough moisture; therefore, it can be a sign of inconsistent soil moisture throughout the season. When there is not enough moisture, the fruit continues to ripen, but without enough calcium it will not develop properly. If you are sure your tomatoes are being consistently watered, it is a good idea to have a soil test done to check the calcium and the pH. In addition to tomatoes, this can occur in peppers, squash, eggplant, melons and cucumbers.

Tomatoes that have cracked as they ripen are also suffering from a physiological disorder caused by soil moisture fluctuations. It often happens when we go through periods of very hot, dry days and the water supply to the tomatoes is reduced or cut off. When tomatoes reach the mature green stage of development and the water supply changes, they will start to ripen. The outer skin of the fruit becomes thicker and more rigid to protect the tomato during and after harvest. If the water supply returns after the tomatoes have begun to ripen, the plant will resume translocation of nutrients and moisture into the fruit. The fruit will start to enlarge and splitting of the skin will occur and leave cracks in your tomatoes. The single best way to prevent this is to be sure that your tomatoes receive a consistent and regular supply of water. You can also apply a layer of organic mulch to the base of the plant. This will act as a buffer and keep the tomatoes from drying out as quickly. It is especially important to water thoroughly every week when the tomatoes are maturing. There are some varieties that are resistant to cracking, but they have a tougher skin.

For more information on common tomato disorders, you can contact your local extension office. Atlantic County residents can contact the Master Gardener Helpline at 609-625-0056. Cape May County Residents can call 609-465-5115, ext. 3607.

Atlantic County Master Gardeners will be available to answer gardening questions and take samples for plant identification or diagnoses throughout the county this summer. You can find us at the Ventnor City Farmers Market: Aug. 9; Atlantic County 4H Fair: Aug. 8, 9, and 10; Brigantine Green Fest: Aug: 24; and Hammonton Green Day Festival: Septl 21.

Do you have a gardening related question you would like answered here? Please forward your questions to Belinda Chester, Master Gardener Program Coordinator, Rutgers Cooperative Extension Office, 6260 Old Harding Highway, Mays Landing, NJ 08330. You can also submit questions at or email them to Please include “garden question” in the subject line.

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