Posted: 10/05/2015 at 18:25
I grow good carrots in raised beds. Because the soil stays loose and doesn't get compacted, it suits carrots very well. The beds are only about 45cm deep - the soil level being lower than this - and this is not high enough to keep off the carrot fly, although it's a good height for most purposes.
So I use horticultural fleece. It's not pretty or convenient, but it works. You can use pegs to secure it, but I now find the best way is to lay a length of fleece across the bed, allowing plenty of spare, and weigh it in place with bricks on the ground outside the bed. That way, as the plants grow, the fleece can be loosened off so that it doesn't squash the leaves. You might need a peg or two to secure it in the middle of the bed and stop the fly getting in the sides.
Fleece varies in quality and it's worth getting a strong quality that won't get torn apart by wind or rain. Last year I had no carrot fly at all, although there's usually a bit of damage by the end of the season.