Grass seed thrives in sun-drenched lawns, but trees and buildings can cause large patches of shaded areas. Add poor drainage or just-damp soil to the mix, and your choices are limited for lush grass seed. In the case of shading caused by trees, you can always prune or thin the tree's canopy to allow more sun to reach the lawn, but this is not always feasible. A better option is to look for grass seed that does particularly well in damp, shaded lawns.
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Perennial ryegrass varieties do well in light shade and wet conditions with at least some drainage. Ryegrass varieties do not tolerate dry, hot weather or harsh winters well. Perennial ryegrasses can adapt to other soils and shade levels, if you expect conditions in your lawn to change over a period of time. Some varieties of perennial ryegrass to try are All Star, Elka and Regal.
Rough Stalk Bluegrass
Rough stalk bluegrass tolerates light and moderate shade levels and enjoys wet conditions. Rough stalk bluegrass does not handle summers well if it does not get enough moisture. It can also leave dead patches in sunny lawns, so you should not count on rough stalk bluegrass if parts of your lawn gets full sun. Rough stalk bluegrass is the grass to try if you have used other grasses unsuccessfully in your wet, shady lawn. Varieties to try include Colt, Laser and Saber.
To capitalize on the best features of both species of grass, the University of Missouri Extension recommends mixing rough stalk bluegrass and perennial ryegrass. Ideal proportions are 50 to 70 percent of the mixture as rough stalk bluegrass seed and 30 to 50 percent perennial ryegrass seed. The extension suggests using two or more varieties of perennial ryegrass seed to give your lawn the best chance at establishing itself in your shady, damp lawn.