Answer: It sounds as if your tomatoes have yellow top - also called green shoulders, says Mark Bennett, vegetable crop specialist at Ohio State University in Columbus. The tomato fruits grow normally, but the tops don't develop their full color and the tissue is hard and inedible. This problem is partly due to genetics and partly due to high temperatures during fruit development, he notes. Tomatoes with poor foliage cover tend to be most susceptible. The sun hitting directly on the fruit surface can raise the temperature of the fruit 20 F to 30 F above ambient air temperature. When temperatures go above 100 F on the fruit surface during ripening, the chlorophyll is slow to break down in those areas, Bennett explains. Try growing indeterminate varieties that have good foliage cover to shade fruits. Celebrity and Mountain Spring are good choices. Or use a shade cloth to cover exposed fruits during particularly hot summer weather, advises Bennett. Minimize pruning and keep plants disease-free so that the foliage stays on the plant throughout the growing season.
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