Provide a high-nitrogen liquid feed each week in June, then a high-potash fertiliser each week from July to September. Once the first frosts of autumn have blackened the foliage, carefully lift and clean the tubers and allow them to dry naturally indoors. Place the dry tubers in a shallow tray, just covered with slightly moist potting compost, sand or vermiculite. Store in a frost-free place, checking frequently over the winter months.