Mel's Mix was created for Square Foot Gardening and if you can afford it, it's a good way to go. This is a light mix that won't get compacted in the beds; if your compost was 'cooked' hot enough there will be very few weed seeds; and the mix drains well so the roots won't get waterlogged.
You can buy the expensive bag mix or create your own:
one part vermiculite
one part peat moss
one part compost...the compost should be made of a variety of plant material to assure more balanced nutrients.
The biggest expense is the first season when buying the vermiculite and peat moss. Next season you just have to add compost to bring the 'soil' up to the correct height - and you can make the compost yourself for free.
