If you're not in a hurry, let nature do all the work by cold composting. Just pile on garden debris, and wait several months to a year. With rainfall helping the materials decompose, the pile will gradually shrink to about half its size. When you want to harvest the compost, peel away the loose debris on top; underneath will be the dark, crumbly material that gardeners consider gold. This hands-off approach, however, doesn't kill weed seeds or disease organisms, so you need to be careful about what you compost.