Study your bank's unique microclimate. Note the location of sunny and shady areas. Is the ground toward the bottom of the slope moist? Is moss growing naturally? Choose your plants based on the unique needs of your space, noting that cold air tends to sink, so hardy plants should be chosen for cooler, moist conditions.
Cut down into your soil with a hand trowel to dig a 3-inch sample near the top of your bank. Try to take the sample away from decaying plant matter, if possible. Place the sample in a clean container and label it "top." Take a second sample from near the bottom of the bank in the same matter and label it "bottom." A sample from either end helps determine the amendments that may be needed to your soil to optimize growing conditions; since runoff has probably occurred, the soil is probably different on each end. Take the samples to your local agricultural extension office for testing.
Purchase soil amendments as recommended per the testing. Manure and compost can be substituted for most commercial fertilizer unless your testing discovered a large deficiency in a particular mineral.
To prepare the bed, kill sod, if applicable, with a herbicide per the package's instructions.
Work amendments into the soil by turning the soil with a spade 12 to 18 inches deep. Continue working the soil until it develops a powdery consistency, using a garden hoe if desired. Unlike flat spaces, where tilling the garden is recommended, slopes are not safe for heavy machinery .
Plant first garden focal points, such as flowering bushes, for example, rhododendrons and azaleas. For an eye-pleasing design, plant an odd number of bushes.
Dig planting holes like a basin in the side of the slope to allow plants to grow down correctly. Stagger holes instead of planting in a line to help with better root dispersion. Consider native wildflowers and ground cover. Native plants provide food for the animals and insects in your area, take up less nutrients and look great when left to naturalize. Consult your local garden center, agricultural extension office or gardening club for ideas on interesting perennials native to your area.
Finish off the space with rocks of various sizes and organic mulch. Ground cover looks great creeping over boulders, and a fern tucked between a rock grouping will look like it grew there naturally. Using an organic mulch such as compost or bark will prevent weeds, retain moisture and give a nice look while breaking down to provide needed nutrients.