Selecting the correct ground cover for a hill or steep slope will mean soil retention. Soil will erode from a bare hill quickly in heavy rains. Plants that are propagated by seed must be fast-growing, and have the ability to place their root system deep into the soil. Transplanting seedlings may not be ideal for the initial selection, as these types of plants will take time to overcome planting shock and reduce erosion. Your own local climate and time of year will also play a part in selecting the correct ground cover for a hill.
Determine the time of year that the ground cover is to be planted and grown. On extremely steep hillsides, the ground cover seed will need to germinate quickly to withstand seasonal rains. Plant annual grasses as the initial seed; in this way the grass will die back and your other ground cover plants will take over. Warm-weather annual grasses may require some form of moderate irrigation for germination. Cool-weather annual grasses will require a thick broadcast of the seed so it can germinate quickly in the cool, moist environment of spring or fall. The freezing cold of winter may not be viable for seed planting. In those cases, a layer of straw 2 to 3 inches thick may have to be spread to reduce erosion from winter precipitation.
Conduct a soil test on the hillside. Collect soil from several locations. Mix the soil together and dry. Deliver the sample to your local agricultural extension service for analysis.
Use the soil sample test results to identify problems with the soil and what types of amendments are required. In some cases, you can match the soil type with certain species of ground cover plants that will thrive in that location. Many ground cover plants will require either a full exposure to sun or just the opposite, full shade. Match the plants with the amount of sunlight available on the hillside.
Consider the irrigation requirements that some ground cover plants may need. Bushes may require irrigation throughout a dry spell. Vining and creeping ground cover plants may tolerate drought, while still others will thrive in a wet area.
Establish the ground cover so the plants have plenty of time to take hold in the new surroundings prior to winter. Plants that are not well established may die from a severe winter freeze.