Once your garden is planted, it will generate large amounts of organic waste--material you can easily turn into rich compost and return to the soil. The simplest composting method is the familiar backyard pile, but you can also use various kinds of bins or, if your space is extremely limited, even a box of worms.
A simple compost pile
For this method, you'll need a space about 10 feet square. Divide the area roughly in half. On one side, alternate 6-inch-thick layers of "green" and "brown" material. Green material includes grass clippings, soft shrub cuttings (chop up any large pieces), some pulled weeds, and the like; brown material includes dry leaves, used potting soil, wood chips, and sawdust. This fifty-fifty green-brown mixture helps maintain the carbon-nitrogen ratio optimal for decomposition. Aim for a pile that's about knee-high. If you're short on green material, add alfalfa pellets; if you're short on brown, add straw (not hay, which contains weed seeds). Both are available at feed stores.
Once a week, mix and turn the pile, moving it to the other side of the space. In about a month, you'll have coarse compost. If you want a finer texture, continue mixing and turning for another month or two. In dry weather, hose the pile down when you turn it; it should be kept as moist as a squeezed-out sponge.
Note that this method requires you to have sufficient material for the entire pile at one time; you can't add new material until the current batch is finished.
A Compost Bin
If you don't have much space available or want a tidier compost-making enterprise, a bin is a good solution. Like a compost pile, it relies on you gathering a fair amount of material all at one go.
The simplest bin is a cylindrical wire enclosure, but cylinders made from flexible plastic with many round holes for aeration are becoming increasingly popular. Fill the bin with 6-inch layers of green and brown materials, as described above; you may also want to include vegetable and fruit scraps from the kitchen. To speed up decomposition and produce a finer-textured final product, chop all material into 1- to 2-inch pieces.
Once a week, lift off the cylinder. Lift and turn the compost-to-be to aerate it; then fork it back into the cylinder. You'll have finished compost in 3 to 4 weeks.
A Classic Composting System
Another composting system is a bit more complex than a compost pile or bin, but it's a very practical choice in the long run, since it allows you to add new material as it becomes available. The system has three sections. The left bin holds new green and brown material, the center one contains partially decomposed material, and the right bin holds finished compost. Turn the material in each bin weekly, moving decomposed material to the right. (The last bin will be empty for a few weeks at the very start.)
For gardeners with no room for a traditional compost pile or bin, worm composting is a solution. Red worms live in a covered wooden box filled with shredded newspaper. You feed them kitchen scraps, and every few weeks they repay you with a box of rich, fine compost. Worms and supplies are available at many garden supply centers.