Answer: What you describe sounds like blossom end rot. Blossom-end rot is a physiological disorder caused by a lack of sufficient calcium in the blossom end of the fruit. This disorder results in the decay of tomato fruits on their blossom end. Dry brown or tan areas the size of a dime, that grow to the size of a half dollar, characterize this disorder. This disorder is usually most severe following extremes in soil moisture (either too dry or too wet). To reduce blossom-end rot in tomato, implement the following steps: Fertilize properly -- Applying too much fertilizer at one time can result in blossom-end rot. Since your plants are in containers, I suggest using a half strength dilution of a water soluable fertilizer (such as Miracle Gro) every 2-3 weeks. Mulch plants -- Use straw, pine straw, decomposed sawdust, ground decomposed corn cobs, plastic, or newspapers. Mulches conserve moisture and reduce blossom-end rot. Irrigate when necessary -- Tomato plants require about 1.5 inches of water per week during fruiting. This amount of water should be supplied by rain or irrigation. Extreme fluctuations in soil moisture result in a greater incidence of blossom-end rot. Spray calcium -- The plants may be sprayed with a calcium solution at the rate of 4 lb of calcium nitrate or calcium chloride per 100 gal of water (or 4 level Tbs per gal of water). This spray should be applied 2 to 3 times a week, beginning at the time the second fruit clusters bloom. Several brands of foliar spray materials containing calcium are available and all work well for tomatoes. Best wishes with your tomato plants!
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