The Q&A Archives: Blossom End Rot on Desert Tomatoes

Question: I've read numerous Q&A on BER. You speak of keeping soil moist. I've been told by desert gardeners that tomatoes shouldn't be overwatered and to allow the soil to dry out between waterings. I use a good forest mulch, bone meal, and water deeply about once a week, sometimes more often as temperatures go up to 100's. I continually have problems with BER, despite different watering methods. Which is correct for the Arizona desert? Neither appears to be too effective. Plants are large, healthy and have had lots of tomatoes, and now are developing early signs of BER.

Answer: The "douse and dry" cycle IS appropriate for native desert plants. They've adapted to an environment of deluge or drought, but modern tomato varieties aren't adapted to this treatment. How often you water should be determined by your soil and how well the water drains/holds moisture, not by a general guideline such as "let the soil dry out between waterings." Your plants' response is the only reliable evidence you have that you're doing things correctly. It's consistency in the moisture level that is important - too much /too little water or an inconsistent watering schedule can lead to trouble. Your goal is to balance air and water in the soil to optimize plant health.

BER is the result of interference in the uptake of calcium. In some soils, calcium is present in a form that plant roots can't take up, even though moisture levels are kept consistent. If you find that, despite your careful watering schedule and attention to the "feel" of the soil, BER still occurs, have your soil tested for soil calcium and pH levels, or use a foliar spray to supply the needed calcium (available from Gardens Alive, 5100 Schenley Pl., Lawrenceburg IN 47025; 812/537-8650). Best of luck beating BER!

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