Prevent Blossom-End Rot by Watering Deeply and Regularly

While out harvesting your tomatoes this season, did you notice any fruits that had round, sunken, water-soaked spots on the bottom?  This is a common disorder called blossom-end rot.  As the name implies, it always occurs on the blossom end of the tomato, opposite the stem end.  You'll often notice it after a few very hot days

Symptoms of Blossom-End Rot

The first symptom is usually the appearance of a small spot at or near the blossom scar of green fruits.  As the spot enlarges, the affected tissues dry out and become light brown to dark brown.  The area then develops into a well defined sunken spot, with the tissues collapsed and leathery.  The spot can grow large enough to cover the entire bottom half of the fruit.  The skin remains unbroken because it is the tissues beneath that have dried out and collapsed.  The disorder not only affects tomatoes, but can also occur on peppers and squash. While the fruit looks unappetizing, you can still eat it - just cut out the affected part. 

Causes of Blossom-End Rot

Blossom-end rot is not caused by an insect or disease organism, so fungicides and insecticides will not work to control the problem.  Instead, blossom end rot is caused by a number of environmental conditions, especially those that affect the supply of water and calcium in the developing fruits.  When rapidly growing plants are suddenly exposed to hot, dry conditions, insufficient water is absorbed by the plant's roots and water and calcium are not transported up to the rapidly developing fruits.  This results in blossom-end rot.  Anything else that reduces the ability of the tomato plant to take up water will also increase injury due to blossom-end rot.  For example root rots, nematodes, lack of aeration due to soil compaction, overwatering, underwatering, overfertilizing, high soil salinity and root damage caused by cultivating too close to the plant may all contribute to the disorder.

Tips for Preventing Blossom-End Rot

There are several things you can do to prevent the calcium deficiency, and blossom end rot.  First, water deeply, and on a regular schedule, especially during hot weather.  Use a soil-covering mulch around your plants to conserve moisture, especially if your soil is sandy.  If you are growing tomatoes in containers filled with a porous potting soil, you may need to water the plants every day during hot periods.  When cultivation is necessary, it should not be too near

the plants nor too deep, so that valuable water absorbing roots remain uninjured and viable.  The best way of preventing the disorder is to maintain adequate and uniform soil moisture in the root zone throughout the growing season.

More Questions about Vegetables?

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References

UC IPM http://ipm.ucanr.edu/PMG/GARDEN/VEGES/ENVIRON/blossomendrot.html 

Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County where he worked for over 30 years.