Pick carefully so as not to break the vines. Do not leave overripe pods on the plants. New potatoes may be dug up when the flowers form on the plant. Wait until the top growth starts to die back for fully grown tubers. If you want to store the tubers for a prolonged period of time it's advisable to wait until the crop matures.
Mature tubers have a firm hard skin and are less susceptible to injuries and store well.
It is best to harvest before the first killing frost. If the growing season is too short to mature the tubers naturally, the top of the plant may be killed to aid maturation. The skin will harden sufficiently if tubers are left 10-14 days in the soil. Wait until the fruit is a deep orange. The easiest method to determine ripens is to sink a fingernail into the rind.