I have always grown leeks from plug plants, as it just makes it so much easier. Ultimately you need to earth up soil around the bases of the leeks to blanch the stems, and so to facilitate that I find it easiest to plant my plug plants at the bottom of a trench. Dig the trench about 20 cm wide and 15cm deep. In Auguest/September plant your plug plants at the bottom of the trench and water in well. When they have grown a bit you should be able to earth up around the base, and continue doing this as they grow. When doing this, try and make sure you don't get soil down inside the layers, as this will be in there when you come to harvest and eat them. They should be ready by Feburary time, but the longer you leave them the bigger they will grow. To harvest them, pull the soil way from the base, grip the base and pull straight up.