We've had a wonderful extended fall here in CT. Above are some of my sweet potatoes. You want to wait to harvest sweet potatoes till the vines start to die and turn black. Usually that happens with the first frost. The reason is, while the vines are still green and vibrant, they are still growing your sweet potato tubers, making them bigger. The first frost also tends to add sweetness to certain vegetables. Carrots, parsnips and collards are good examples. We had a frost here last friday night and the sweet potato vines turned black, so saturday i harvested the sweet potatoes. It was a good harvest. Got over 200 potatoes from one 30' row. Some you might want to eat right away, but a lot you'll want to save to eat over the next few months. Best way is to harvest them and lay them out in the sun for the day. Being in an urban area, if i did that, i wouldn't have any left the next day! So, next best method is to brush off as much dirt as possible, and lay them out in an airy place for a week to 10 days. Don't wash the sweet potatoes before you cure them, you are letting the skins get a bit tougher and that will protect and help keep the sweet potatoes for a longer time. Store only those potatoes that you haven't cut in 1/2 while harvesting, or have other deformities. Whole, blemish free potatoes will store the best. Store them at around 55 to 60 degrees with about 85% humidity. They will keep for you all winter long this way. If you don't have a cellar you can store them in, try keeping them in the fridge.