Supposed to be about 2ft isn't it? I thought I'd have a go with this old bath our friends gave me, so I put some crocks in the bottom, especially around the plug hole so it doesn't get waterlogged. Filled the bottom half with old hanging basket compost, then soil on top, and becausde weve had so much rain, its still waterlogged!!! Could be because its sat on the ground, must et up there and jack it onto bicks or something, or dig out watery soil and start again.
I'm also going to try the idea of putting fleece around them this year, but last year it wasn't so much carrot fly I had trouble with, it was just the germination rate, and I waited til the weather got better too!!!