Gardening with Gary

Gardening Advice from an Expert

Blossom-End Rot

Q. Would you tell me what causes blossom end rot, and how to remedy it?

A. Blossom-end rot is a common disorder that occurs on tomatoes, peppers, eggplant, and some melons. It is a symptom of calcium deficiency in the fruit. It may be caused by low soil calcium, low levels of calcium in the maturing fruit, or other cultural factors -- particularly fluctuating soil moisture. This disorder is usually most severe following extremes in soil moisture (either too dry or too wet). These conditions result in a deficiency of calcium available to the maturing fruit, at the spot where damage becomes apparent. Blossom-end rot is most prevalent on tomatoes. The affected fruit areas become infected with secondary pathogens, which appear as black, felt-like Applying lime several months pre-plant to low-calcium soils can help prevent blossom-end rot. Foliar sprays of calcium won't correct blossom-end rot once it has occurred on the fruit.

Cultivars that grow quickly and produce large amounts of foliage tend to be more susceptible to blossom end rot. Therefore, reducing nitrogen levels will help reduce blossom end rot. The use of 5-10-10 fertilizer in place of 10-10-10 or 13-13-13 on tomatoes will help reduce the nitrogen problems associated with blossom-end rot.

Fluctuations in soil moisture during periods of rapid plant growth create moisture stress and limit calcium distribution to the fruit. Plant a bit later in the season to reduce the problem. Removing affected fruits when symptoms are first observed may promote subsequent sound development of other fruit on the plant. By the time a second set of fruit begins developing, the plant has an expanded and developed root system capable of gathering and delivering calcium to the fruiting structures.

In order to control blossom-end rot, the following steps should be taken: Select sites that have deep, well-drained soils. A large well-formed root system is better able to take up calcium and other minerals. Tomatoes and other susceptible crops grown on land that has not been limed for two years or more are prime candidates for blossom-end rot. Soil test to determine soil pH and soil nutrient levels annually and adjust the pH to 6.5 as needed. Maintain soil pH between 6.0 and 6.5 Don't over fertilize tomatoes when planting them. Mulch plants to conserve moisture and to provide a more uniform water supply. Straw, pine straw, ground leaves, or newspapers are all good mulches. Mulches conserve and maintain a uniform moisture supply, thereby helping to reduce blossom-end rot. Under drought conditions, plastic mulch may overheat the soil and increase blossom-end rot if plants are not watered properly. Adequate soil moisture throughout the season through mulching and water management is essential for avoiding the disorder. Avoid cultivation and hoeing. If cultivation is necessary, it should be shallow to avoid root pruning. Avoid severe pruning. Severely pruned tomato plants are more prone to develop blossom-end rot than unpruned plants.

Keep water supply uniform and regular. Irrigate plants thoroughly and often enough to maintain a constant water supply without water-logging the plants. Extreme fluctuations in soil moisture can cause an increase of blossom-end rot. Preventing moisture stress is important to control blossom-end rot, especially during fruit set and fruit enlargement.

Acknowledgment is made to The University of Georgia and Ft. Valley State College http://www.ces.uga.edu/Agriculture/horticulture/blossom-rot.html