Some gardeners would love to have your problem, because lily-of-the-valley (Convallaria majalis) is regarded as a wonderful blooming ground cover for moist, shady spots. In the upper Midwest, however, lily-of-the-valley grows so well that it is now listed as invasive. To replace your patch with something better behaved, such as hostas, begin by killing the lily-of-the-valley with a nonselective herbicide such as glyphosate (Roundup) or by digging out all you can. Herbicide-treated plants should die within a week or two. If you choose instead to dig plants, lay the plants and roots in the sun for several days before dumping them on your compost pile. After a few weeks, expect a number of new sprouts to emerge in the patch. Treat them again with herbicide or dig out the newly emerged shoots. After replanting the spot, patrol for stragglers for a year or two, because seeds may continue to sprout.