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But it can take 70-90 or more for potatoes to mature. This depends on the variety. The potatoes can carefully be harvested at 7-8 weeks for a early harvest of small potatoes. For full grown potatoes you would harvest in the fall when the leaves turn brown. But it can take 70-90 or more for potatoes to mature.
When to harvest sweet potatoes depends largely on the seasonal growing. If the growing season has been good with adequate water and sunshine, harvesting sweet potatoes should begin about 100-110 days after planting depending on the variety. A good rule of thumb is to watch for the first signs of yellowing leaves.