A really handy way of growing quite a variety of vegetables etc is using the black plastic 'flower' tubs (in which supermarkets receive their cut flowers and which most of the said supermarkets either give away or sell at a few coppers each).
These are around 10" or so high, and once pierced in the bottom (ooh, matron) with a hot screwdriver or similar for drainage can be used to grow loads of things (although not all that good for brassicas or roots needing an especially deep space).
Certainly excellent for salad leaves, carrots, runners and peas, courgettes (with a load of watering!), potatoes, leeks, outdoor toms and peppers, herbs....
Now, you can sit these into 'islands of sevens (six in a circle, touching, with one in the middle) and create wooden walls around them c 16" high. An inch or two of coarse gravel in the bottom, stand the pots in, infill with (non-salty) sand and a thin layer on top of shredded bark mulch if you must. They look good - and with careful succession planning you can start stuff off elsewhere and swap out the pots when the previous ones are going over.
You are not limited to the hexagonal arrangement - can combine two of those clusters and fill in a long 'bed' in between, with smaller pots slotting between the edges and the pots in the 'half pot' gap areas. NB. If you fill these smaller pots with long flowering period plants such as french marigolds and trailing lobelia etc they really brighten up the area beautifully!
Thorough, consistent and regular watering though is key!
As suggested elsewhere, a coat of dark paint on the outsides finishes them off nicely.
