I think the temperature patern is a factor in potato maturity. That means, if in one place days highs are 75F and nights lows 50F and in another location they are 85F and 60F, then potato plants will mature in shorter time in the latter. But generally, potato plant will mature in 100 to 120 days; That is from sprouting out of ground till harvest. In zone 7/8 (GA) I planted in early March.But we have had a lot of cooler days/nights. So I expect to harvest early in July. I can (hopefully) reach in and get young potatoes from early June on. The flowering and stem texture can tell that too. As the plant gets near harvest time, its stems become woody and turn light brown or pale green. But the best indication will be on the potatoes that you dig out. The skin should be harder and will look like store bought ones. But as long as there is no danger of frost, and plants top have some life, I would leave them in the ground longer.

chudh - For future endeavors, you can take one potato, and submerge about the bottom third of it in a glass of water. You can stick toothpicks in the potato about a third of the way down and rest the toothpicks on the glass. The potato will begin to sprout. After the sprouts are about 6 inches long, you can pop them off of the potato and put them in water and they will make roots. These small plants are called slips, and you can make multiple slips from one potato. In fact, I have a barrel of sweetpotato plants growing in my garden right now that all came from one potato. I didn't throw it out when I finished and now my kitchen window is filled with potato vines. You will have to add more water to your glass from time to time. Easy to grow.

My red norlands did not flower at all. People here say to wait until the plant fully dies back and leave them in the ground a couple more weeks for thicker skins that store well, I didn't have issues storing my potatoes dug up as the plant was dying, for a few weeks at least, but I think it depends on the variety. If you are harvesting a ton of potatoes you want to store a long time then you should wait.

That is the way most potatoes are planted, by cutting the eyes off a potato (with a piece of the potato) and planting it into the ground. They are fine that way, I have done that for years and no ill effects, just great tasting potatoes. Although some varieties of potatoes bloom and may produce small seed resembling a small tomato (which I have heard is poisonous) the term "seed potatoes" usually means potatoes from fields that have been certified as disease free. They usually cost a lot more than potatoes that you buy at the store. Most people cut those up in chunks with one to several eyes on each piece and let the age for a couple of days to heal the cut part over some before planting. I have used both kinds, store bought and seed potatoes that I bought at feed and seed stores, with just about equal success, but some feel a lot more comfortable when buying certified seed potatoes. A simple google search with the words POTATO SEED will turn up much information about the subject. I think that there are some people working on developing potato seed, rather than seed potatoes, to save in shipping and storage cost to third world countries to they to help them, but could be wrong on that. Good luck with your efforts to grow potatoes and post any further questions that you may have. Bill P.