it is time to harvest potatoes. i find it not easy to know when they are ready, as you can´t see the fruits your looking for. so you have to look at the plants. i think it depends a little bit on the kind of potato but for sure you have to wait until the blossom is over. between this time and the point when the plant starts to wilt, they are ready.
displant the greens and start to burrow. you should find the potatoes between ground level and 10 cm depth. one potato plant will have between 4 to 6 potatoes, sometimes more and sometimes less.
potatoes are the ideal vegetable to store (do not wash them before you store them). all you need is a cellar with a constant low temperature and a large box. if everything works fine you can eat your homegrown potatoes until the end of winter.