Preventing Blossom End Rot in Tomato

Janet McLeod Scott
Home & Garden Information Center

The tomato is easily the most popular plant grown in many home vegetable gardens. Blossom end rot is a common problem that gardeners encounter when growing tomatoes. This problem is not caused by a disease organism, but is rather a physiological disorder that results when there is an inadequate supply of calcium available to the developing fruit.

Image depicts tomatoes with blossom end rot.
Blossom end rot on tomato
David B. Langston, University of Georgia, Bugwood.org

Initial symptoms of blossom end rot generally appear as water-soaked areas on the blossom end of the fruit (the end of the fruit away from the stem). Over time the damage becomes a sunken, dark-colored rot (see above). Secondary decay-causing organisms will often infect these areas.

While the occurrence of blossom end rot may indicate calcium deficiency, in reality, the soil may have adequate calcium. However, for various reasons the plant may not be able to take up enough calcium to supply the rapidly developing fruit. As a result, efforts to manage this problem fall into two categories: pre-plant and post-plant.

Prior to planting, the main preventative measure is to have a soil test done to determine if adequate calcium is present in the soil. Limestone (a source of calcium) should only be applied if soil test results recommend it. When a need for limestone is indicated, best results are achieved when the limestone is worked into the soil 2 to 3 months prior to planting.

After tomatoes are planted, gardeners can minimize the potential for blossom end rot by doing the following:

  • Once transplants become established, encourage the production of a large root system by keeping plants a little on the dry side for a few weeks (until they begin to flower and set fruit). A large root system is better able to take up the calcium needed for the healthy development of the tomato fruit.
  • After fruit set begins, keep soil evenly moist. (Avoid extreme fluctuations in moisture levels. Do not overwater!)
  • Apply a layer of mulch to help maintain even moisture and keep soil cooler.
  • Do not overfertilize. Especially avoid high-nitrogen fertilizer as it can cause problems with the uptake of calcium.
  • Do not cultivate closer than 1 foot to plants to avoid damaging roots.

If tomatoes develop blossom end rot, spray the foliage with calcium chloride or calcium nitrate when symptoms first appear. Follow the instructions on the label. Removing fruit with symptoms is also recommended.

The good news is that tomato plants self-adjust after the first fruit are set, and later fruit are typically not affected by this disorder.

In addition to blossom end rot, there are several diseases and insect pests that can be a problem on tomato. If you are interested in learning more about what it takes to grow healthy tomatoes, see HGIC 1323, Tomato. For more information on other tomato problems, see HGIC 2217, Tomato Diseases and HGIC 2218, Tomato Insect Pests.

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This information is supplied with the understanding that no discrimination is intended and no endorsement by the Clemson University Cooperative Extension Service is implied. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.