As water flows down a slope, it can erode the soil, carry fertilizers and destabilize plants on the grade. As a result, slope gardens demand a bit of extra planning and care. Slopes also add interest and individuality to your garden, so the extra work they require is well worth the effort.
Stabilize your sloped garden without terracing and give it a unique look with a rock garden. Embed a number of landscape boulders into the ground and mulch the area between with gravel to slow down erosion. Grow plants that do well in rocky soil between the boulders. Ferns, alpine plants such as purple fringe, mosses, lichens and many other plants will grow either on the boulders or in the spaces between.
Plant the slope with a wide variety of plants with strong root systems that can hold back erosion. According to Today's Garden Ideas, your garden should have plenty of woody shrubs such as azaleas. Combine these with trees such as wild cherry, flowers such as catmint and geraniums and other plants that hold soil well.
Use retaining walls and other hardscape features to prevent erosion. If your garden is not on too severe of a slope, build a stone staircase or walkway to prevent foot traffic from contributing to erosion and erect a single retaining wall near the bottom if necessary. If your garden is on a steeper grade or is especially prone to erosion, divide it up into several terraced levels using retaining walls. This will prevent dirt from washing downhill when it rains, greatly reducing erosion. If your garden is impractically steep, level the grade and cover it with a patio. Create a planter garden on the patio or install raised flower beds around the edge.