In article , Janet Tweedy
writes
Now I've managed to build nearly all 12 raised beds at the top of my
garden (a scaffolding plank long and 4 foot wide) I would like to cover
at least part of one or two to start early crops.

Can anyone with more experience of growing vegetables this way suggest
the best/most efficient means of warming the soil and/or growing under
plastic/fleece?

If we want to push a raised bed on a little early, we cover it after
seeding with a sheet of clear PVC. We weight the sheet down to prevent
it blowing away and we remove it as soon as small seedlings can be seen
pushing up under it. That reduces germination and growing time by 7-12
days depending on circumstances.
--
Alan & Joan Gould - North Lincs.