Posted: 15/08/2013 at 20:46
Whatever you use it should let water through, black plastic is no good. I use a sort of woven fabric, which isn't cheap, but it lasts. I cut long thin holes for planting peas in rows, far apart big crosses in it for planting courgettes, cucumbers and butternut squashes and fairly close together crosses for planting onion sets, crosses a little further apart in rows for French beans. I leave the fabric in the winter and remove in the spring for digging and manuring, then replace it, rotating for crop rotation. I don't use it for potatoes because of earthing up or leeks because of trying to dig them up in winter. Great for tomatoes too. It keeps the moisture in and I haven't noticed any extra pest problems. In fact I think there are fewer slugs because they dn't like crawling over it. Mine comes in metre wide rolls and you peg it down with big metal staples or tent hooks.
Why don't you ask the other allotment holders where they got theirs?