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Controlling blossom end rot in the vegetable garden

Our tomatoes are just starting to grow and it’s possible you are seeing the beginnings of blossom end rot. Blossom-end rot (BER) is fairly common and occurs on both tomatoes and peppers but can also be seen on eggplant and the cucurbit family. It is caused by a lack of available calcium to the fruit. This deficiency is due to low soil calcium or other cultural factors — mostly fluctuating soil moisture. Tomatoes don’t do particularly well in constant wet/dry periods, they prefer a constant soil moisture but not too wet.

The first visible symptom is a small water-soaked area around the blossom end of the fruit (opposite the stem for first time gardeners). This usually appears about the time the fruit begins to ripen. The spot will darken, enlarge, and become sunken as the fruit matures. Large lesions often show concentric rings. The affected tissue is leathery and firm unless invaded by other rots.

A few fruit disorders resemble BER that can sometimes cause confusion. Anthracnose, for example, occurs in both tomato & pepper but the lesions are on the sidewalls of the fruit not the blossom end. The same is true for sunscald in peppers but it also appears on the sidewalls and is a lighter color. BER is uniformly dark brown or black and appears ONLY on the blossom end. Sometimes symptoms will occur a third to half way up the fruit but will never start at the stem end.

Calcium is taken up by the plant and travels throughout with the water. As a result, any interruption of the water supply to the plant may cause a localized calcium deficiency in the blossom end of the fruit. The physiology of the plant can also contribute to the problem.

Most water is lost (transpired) through the leaves and, as a result, most of the calcium is found there, especially during hot, dry weather. Relatively little water evaporates from the fruit and therefore, less calcium is deposited there. Add to this the fact that calcium is immobile in the plant and the possibility of problem becomes a reality. What can you do to reduce chances of having a problem with blossom-end rot?

  1. Select sites that have deep, well-drained soils. A large well-formed root system is better able to take up calcium and other minerals.
  2. Soil test to determine pH and soil calcium levels. Maintain soil pH between 6.0 and 6.5 and soil calcium levels at or above 400 lb. calcium per acre for our area. If soil calcium is low and the pH is correct, gypsum (calcium sulphate) can be soil applied at a rate of 500 to 1,000 lb. /acre (1.5 to 2.3–lb.\100 sq. ft.) to supply additional calcium. Gypsum can be applied from planting to first bloom, the earlier the better. Lime should be applied in the fall before the spring planting, allowing time for it to dissolve and become active.
  3. Avoid ammonia-containing fertilizers as side dressings. Use calcium, sodium or potassium nitrate for side dressings. Do not apply large amounts of fertilizer at one time – do several small side-dress applications.
  4. Mulch plants to conserve moisture and provide a uniform water supply. Keep water supply constant and regular. Irrigate plants thoroughly and often enough to maintain continuous moisture without waterlogging the plants.
  5. Severely pruned plants tend to have more blossom-end rot so avoid severe pruning.
  6. Foliar calcium sprays can be used to try to prevent or cure the problem, beginning when the first cluster of fruit appears to show signs of BER. Apply sprays according to label directions.

If you have any questions, feel free to contact Brenda Jackson at Murray County Extension at 706-695-3031 or email: .