Connecticut Garden Journal: Lily of the valley and sweet woodruff make perfect ground cover
Often gardeners are in a dilemma about what ground cover to grow around perennials and under trees and shrubs in a shady area. I've got two solutions.
Sweet woodruff (Galium oderatum) is a perfect ground cover for full to part shade. It has fragrant, lance-shaped, bright green leaves all summer and dainty white flowers in spring. It's easy to grow and adapts to a wide range of soil types and moisture conditions. Not only that, it's deer and rabbit proof.
Sweet woodruff spreads quickly, especially in average to wet soil. The underground rhizomes allow this perennial to creep fast, so it can become too aggressive in some yards. Weeding and withholding water will slow its spread, but with some rains it will come right back.
Another shade ground cover is lily of the valley (Convallaria majalis). It's not a true lily, but in the asparagus family. It has large, dark green leaves and fragrant white or pink flowers in spring. It's a perennial that will slowly spread by underground rhizomes to fill an area. It thrives in shady spots and forms a dense carpet of greenery choking out weeds and other plants.
The key with keeping these aggressive ground covers in bounds is planting them in the right places. We plant lily of the valley between a porch and our house foundation so it can only spread in one direction. It's much easier to weed out of unwanted areas this way. Another option is to plant near a deep edging, walkway or other solid border. This will prevent the spread, or at least make it easier to control.