Maintaining lawns on level ground is time-consuming, hard work and expensive. But trying to grow a decent crop of grass on a slope is difficult, can be dangerous and is seldom rewarding. On slopes, the soil is often too thin to support a healthy turf. On slopes, water and fertilizer tend to migrate down-slope, leaving most of the slope dry and hungry. If the slope faces south, expect the slope to function as a lawn-grub nursery. Mother beetles love to lay their eggs on warm, dry, sunny, grassy slopes.
Mowing the grass on slopes requires extra measures of care and caution. If the grass is at all wet, it is common to experience slipping and sliding of the mower or the operator. It is a challenge to maintain a uniform height of cut on a slope. As lawns usually require 20 or more mowings a year, grass may not be the best plant to use on slopes.
What can be used? There are many possibilities, but first an analysis of the area should be undertaken.
Is the location visually important? That is, does the slope lead up from the street or driveway or is it seen from the deck or patio? Is it a down-slope that is not seen from your living areas? The visible slope is sufficiently important so as to spend time designing an attractive planting. Are you interested in a utility planting simply to hold the slope from eroding? Or will the slope become an important aspect of your landscape?
In what direction does the slope face? South-facing slopes tend to be hot and dry, while north slopes are cooler and a bit moist. Investigate the depth of soil on the slope. Is it of sufficient depth to support the groundcovers, perennials, or shrubs that you intend to install? Perhaps the solution to providing adequate soil for planting is to dig individual holes rather than coating the entire slope with soil that will erode.
Does the entire area of the slope enjoy similar light or shade? Ferns, hostas, Epimedium, lily-of-the-valley, Lamium and the well-known and often overused Pachysandra and Vinca all prefer shade and each is available in a variety of sizes and colors.
A half-day or more of sun allows you to broaden your design palette considerably. Dozens of sedums are available for your use. The Sedum spuriums can be selected for variegated foliage, or pink, red, white, or purple flowers. Sedum acre grows an inch tall, covers itself with yellow blooms and spreads more than a foot wide. Thyme reaches two inches high and a foot wide. By making use of flower colors, foliage tones and extended flowering cycles, a flowering Persian carpet can be planted.
Ajuga presents foliage in variegated or solid colors like purple and flowers to blue, purple, pink and white. Juniper and Cotoneaster are but two of the low shrubs that develop deep questing, soil-holding root systems. Euonymous is a spreading vine.
Remove existing vegetation, lime and fertilize, plant and mulch, and water regularly for the first year. Prune yearly as needed. Enjoy not mowing that slope.