If what you use isn't well composted, it will tie up nutrients in your soil, especially nitrogen. This will affect plant performance. Great garden soil builds slowly, not in one season. Mulching every few years with compost will provide enough nutrients for a garden and keep the organic matter of your soil up around 16 percent. If adding organic matter, place 2-4 inches over top of the soil.
Double digging is a good way to prepare a new garden bed.
If you haven't heard of this back-breaking technique, count your blessings. The idea originated from England, the mother of great gardening. After working this subsoil, add back the topsoil and amend it. Basically, you're loosening and improving the soil to a depth of 20-24 inches. Some feel double-digging is worth the effort and the key to making your garden a success.