If you want potatoes for Christmas they should be put out to chit (sprout) now. After they have started to sprout, break off any weak shoots and leave the three strongest to form. Placing the seed potatoes into old egg cartons is a good way to get them to chit nicely. Plant out into the garden when there is little danger of a late frost. Or if you want to plant them out now, dig a trench and place the potatoes into it, cover with about 10cm of soil and continue to cover as the shoots rise above the soil. This not only promotes development of baby potatoes, it helps to protect the shoots from frost.