Answer: Potassium deficiency is most likely your problem, says Hal Rutledge, horticulturist at the University of Tennessee in Knoxville. This symptom commonly occurs in late season tomatoes and is mostly cosmetic, affecting neither the taste nor the canned storage life of your tomatoes, he says. Either there's not enough available potassium in the soil or water stress has prevented the tomatoes from taking up the element. The first step toward a solution is a soil test to check the available potassium level, explains Rutledge. If the potassium is available, be sure the tomatoes are well watered throughout the growing season. Mulch them with straw 4-6" deep to retain moisture. If potassium levels are low, add a fertilizer such as 13-13-13, soybeanmeal or granite dust.
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