This year I thought I'd try something different with growing my leeks. It's important to blanch the lower part that you eat, because the tough green upper part isn't too tasty at all. In other years I've tried transplanting them into deep furrows - and letting the furrows fill in gradually around the stem. They did blanch, but they grew with lots of grit to wash out later! So this year I transplanted them on top of the soil, and let them grow for a while.
Seemed to me, if I could just cover about 10"of the stem, the leaves would grow out the top of whatever I used, and they might end up being blanched, the way I hoped. I finally fixed on using 1litre milk or cream cartons, and I only had one to start with, so I threaded the leaves through it, and secured it to the earth with a landscaping staple.
Worked like a charm! Now I have another six to position tomorrow. The leeks won't be full grown until about November, and I should be able to use them through the winter. They're pretty hardy things. the most interesting thing so far is that the carton covered one I started with is much bigger now than any of the others! You can see this here.