Vinca minor vine, the perennial ground cover with the cute common name of "periwinkle flower," is widely used as a grass substitute in lawn areas. Grown in zones 4-8, Vinca minor vine requires good drainage. This shade-loving ground cover has traditionally been planted under large trees, where the homeowner's choice of lawn grass would quickly have given up, deprived of sufficient light.
Vinca minor vine is a short plant, like the deadnettle mentioned on Page 2, growing only 3"-6" off the ground, but its trailing stems with evergreen leaves spread up to 18". The stems root at the nodes as they creep along the ground and spread rapidly to form an attractive ground cover. Vinca minor vine puts out the bluish-lavender "periwinkle flowers" in spring and blooms intermittently throughout summer. Be forewarned: periwinkle flower is an invasive plant. If the invasiveness of Vinca minor bothers you, use hosta plants, instead.
Northern Sea oats (Chasmanthium latifolium) grows 24"-36" high in loose clumps of green foliage. Its name derives from its seed pods, which look like oats. This shade-tolerant ornamental grass is cold hardy to zone 5.
But what if you wish to landscape a shady area with neither a ground cover nor an ornamental grass, but a turf grass? You need a fine fescue grass. Fine fescue lawn grass seeds often come in bags mixed with Kentucky bluegrass. Buy any lawn-seed mixture labeled "for shade," which includes fine fescues such as hard, chewing, and creeping red. At least 80% should be fine fescue grasses. This shade-tolerant lawn grass grows in zones 3-8. An alternative is the new and improved class of tall fescue grasses known as "turf type" tall fescues.
When planting fine fescue seed in a shady area with trees, first use soil amendments such as compost and peat moss to improve the body of the soil, so that it does not dry out easily. You'll have trouble with your fine fescues if the soil has a tendency to dry out, which is precisely what will happen if tree roots are absorbing all the available water in the area. On the other hand, fescues don't want to be in excessively wet soil either, so you wouldn't want to plant them in an area that is chronically wet. You need to maintain a balance between good drainage and water retention, and applying compost will help you achieve this balance.
In fact, the latter bit of advice applies to any plant that you wish to grow in the shade. Just because it's not as hot in the shade as it is out in the sunny areas of your landscape, don't forget that your shade plants still need to be watered properly. A soil with good water-retention will minimize the amount of time you'll spend watering -- but you still have to water shade plants! Sandy soils need to be amended with organic matter; the latter will slow down the movement of water through the soil, so that your plants have a chance to take a drink.
Finally, resist the temptation to go to the opposite extreme, thinking that there's no such thing as too much water. Most plants need good drainage, because roots sitting in water will rot. Soils with heavy clay have this problem. Again, the answer is to amend the soil, although the problem here is the opposite. In the case of heavy clay soils, amendments will loosen up the soil, allowing water to percolate hrough at a reasonable rate. After all, your plants' roots want to drink, not drown!