Dwarf, set the potatoes up with the eyes upwards in a seed tray with a piece of newspaper underneath, put the seed tray on a window sill which is warm enough but not over a radiator. It may be a week or two before you plant them outside. You can cover the plot in which you want to plant the potatoes with a polytarp set up with large flower pots underneath, this will keep out frost and warm the ground. Do not cover frosted ground. Rocket is a good cropper, I lifted 60lbs. from 30 seed potatoes set with lots of watering and feeding with Tomorite.