Prepare the area for the flowerbed. Remove large rocks and amend soil as needed for plants to grow. Workable, non-compacted soil should exist several inches down to allow roots to develop. Dig holes for flower plantings.
Cover the area with jute netting. Pin jute with landscape pins on corners and in the center for large areas. This material slows erosion immediately and retains moisture needed by growing plants.
Place plant material in holes. Choose flowering plants such as gaillardia, rudbeckia and echinacea that return year after year. Add native shrubs in large flowerbeds, such as Itea, rhododendron and juniper. Native plants need less care than exotic specimens and are drought resistant once established. They help hold the soil in place and slow erosion on the hillside.
Apply organic mulch around plantings. Mulch retains moisture and supplies nutrients to plants as it breaks down. A layer of mulch slows slope erosion.
Border the planted garden with native rocks, or include rock within plantings, if this enhances your design. These may help slow hillside erosion on steep slopes.