Answer: You can harvest sweet potatoes as soon as the leaves start to yellow, but the longer a crop is left in the ground, the higher the yield will be. If frost blackens the vines, though, the tubers will quickly rot. Your average frost date is the end of September, so plan to harvest them before that. (Or, watch the local weather reports and harvest just before the first predicted frost.) Tubers can grow a foot or more from the plant, so be careful as you dig them from the soil. Dry the tubers in the sun for several hours, then move them to a well-ventilated spot at keep at 85F - 90F for 10-15 days. Properly cured sweet potatoes will keep for several months.
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