Frost is a good way to finish the plants. Tubers must mature or cure if you want to store the potatoes for any length of time. Tubers must sit in the ground for 2 - 3 weeks to harden the skin on the tubers. At harvest time dryish soil is definitely an advantage since tubers come up a lot cleaner, but too dry and it will be hard to dig. Avoid scuffing or injuring the tubers during harvest or storage and disease problems could occur.
Harvest is best in the morning when the tubers are cooler.
Place a fork or shovel at the edge of the hill and lift up the hill carefully, avoiding cutting tubers. If the soil is wet, allow the tubers to air dry before sacking them. Field grade or separate to potatoes before sacking them into big and little tubers. Separate any diseased or damaged tubers at harvest and store them apart. These tubers may rot and also rot the good tubers around them in a sack.