Many gardeners choose to enrich the soil in their raised flower and vegetable beds through the use of nutrient-dense compost. Rather than add compost to your raised beds right before planting time, you can easily leave organic waste to compost directly in the soil over the winter season. This process, called sheet composting, reduces the amount of springtime work you have to do in preparation for planting. It also aerates the soil and helps improve moisture absorption. According to Elizabeth Stell, author of "Secrets to Great Soil," you should allow minimally six months for the compost to break down completely in the soil before you plant in your raised beds.
Collect your organic waste in two piles next to your raised beds. Arrange in one heap all the nitrogen-dense materials, which are typically moist, green compost ingredients, such as cow or chicken manure, fresh grass and yard clippings, fruit waste and vegetable peelings. Gather the carbon-rich waste into another pile, including dry, brown ingredients, such as dead leaves, shredded cardboard and newspaper, straw, sawdust and old hay.
Till the soil in your raised beds. Use a hoe or shovel to loosen the top three to five inches of the dirt. Break any large clods of soil into smaller pieces that are less than about one inch in diameter.
Spread a three- to four-inch layer of carbon-rich organic waste across the surface of the tilled soil. Spray the dry waste evenly with your garden hose to dampen it until it's about the consistence of a wrung-out sponge. Top the carbon waste with an equally sized layer of nitrogen-rich compost ingredients.
Sprinkle a one-inch layer of plain topsoil across the double layer of waste; avoid bagged soil since it's typically sterilized and doesn't contain the microbes necessary to jump-start the composting process. Add one more layer of dampened carbon waste and one more layer of nitrogen waste.
Leave the waste to decompose in the soil for at least six months. Watch for the volume of the bed soil to decrease gradually as the microbes break down the waste. Before you plant, till the soil with your hoe to make sure you don't see any signs of the original waste; the compost soil should possess an earth-like texture and smell. Mix the composted soil thoroughly with the soil in the bottom of each raised bed.