You may already know that any garden soil from the heaviest clay to the most porous sand, benefits from regular additions of organic matter – compost, well-rotted manure, peat moss, chopped leaves, grass clippings, or any of the other widely available materials. When gardening in the shade, the extra time taken to prepare the soils will pay off handsomely in healthier plants. For all but the very best garden loam soils, you should add plenty of organic matter before planting anything, from a single azalea to a whole bed of lily-of-the-valley. If your soil is a rich loam, the addition of organic matter will improve its quality even more.
To enrich the soil and improve its aeration and drainage, spread a 2 to 4 inch layer of organic matter on the soil surface. Incorporate the material into the soil to a depth of 6 inches. If the soil is particularly heavy or you are planting a large shrub, work the soil several inches deeper. Plants with roots growing in the deep rich soil will have better overall growth than those plants that are forced to compete fiercely for water and nutrients in shallow, lean soil.