You may know that any garden soil from the most heavy clay to the 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 accessible stuff. The extra time taken to prepare the grounds will pay off in healthier plants, when gardening in the shade. For all but the absolute best garden loam soils, you should add lots of organic matter before planting anything, from an individual azalea to a complete bed of lily-of-the-valley. If your soil is a rich loam, its quality will be enhanced even further.
To enrich the earth and enhance drainage and its aeration, spread a 2 to 4 inch layer of organic matter. Incorporate the substance into the soil to a depth of 6 inches. If the soil is not especially light or you’re planting a shrub that is big, work the ground several inches deeper. Plants with roots growing in the deep rich soil could have better total development than those plants which might be driven to compete fiercely in shallow, lean soil for nutrients and water.