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Often, one can make the finalOften, one can make the final harvest after the plant has died back, unless you desire a smaller sized potato, in which case the main harvest would be earlier, when most tubers have reached the desired size. If you do not have frost in your area, the plant still has plenty of green leaves (along with the new ones), and the plant is not starting to die back (turning brown), then you can certainly let the plant continue to grow and see if it survives to form more tubers.

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