Been thinking of doing this for a while now but am not to sure how to go about starting it

, thought id mention it in here as a lot of yous guys across the water have these kind of things

, i want to make a small allotment in the corner of the garden so how would you go about preparing it ready for planting & also a small choice of vegetables which would have low maintenance, eg:carrots, turnips, beetroot & maybe lettuce if that is along the right lines, would appreciate any help or tips, cheers Simpbow.