We are having an erosion problem with two large boulder walls in our condo association. We want to preserve the looks of the boulders and not cover them up completely, but yet need to retain the soil around the rocks. We thought about vinca, pachysandra, vetch, etc.
There are several ground covers or filler plants that would work well to control the erosion and compliment the boulder wall. The plants chosen will depend on the amount of available light. First review the four categories of light and then choose your plant or plants. All recommendations reflect low maintenance plants that will not completely cover the boulders, help control the erosion and will take dry soil, because of the hill condition.
The four light conditions are dense shade that has no direct sunlight, and is mostly reflected light under trees or evergreens, or against a north wall. Moderate shade is filtered or reflected light with almost no direct sun. Part sun has filtered sun and a few hours of direct sun. A minimum of six hours of direct sun is considered full sun.
Some nice plants for direct to part sun that also have wonderful blooms include the herb thyme (several varieties with fun fragrances like lemon or coconut), hens and chicks (Sempervivum) grown for their succulent foliage, low-growing sedums with red blooms like ‘Bronze Carpet’ or ‘Dragons Blood,’ and candytuft (Iberis sempervirens) with white blooms.
For part sun to moderate shade try the hardy and fleshy ice plant (Delosperma nubigerum) with nice yellow blooms in May.
Plants that will grow in many light and adverse soil conditions include sweet woodruff, which thrives in dense shade to part sun and blooms in spring. Also, several varieties of Lamium that thrive in full sun to moderate shade bloom in spring and sometimes rebloom in fall. My favorite is ‘White Nancy’ which has white blooms in spring and silvery foliage that “glows” in the dark.
Many of the plants mentioned above can be purchased by the flat to make them more economical to plant in large areas.
Of the plants you have already considered there are some things to keep in mind. Vinca spreads easily and will quickly force out native woodland plants if your wall is not in a completely landscaped area. Similarly, vetch is an extremely vigorous invasive plant. Pachysandra, although not as invasive as the other two, is just not very suitable for growing on a wall.
Whichever plants you decide upon, keep them well watered until they get established, and plant with a slow-release fertilizer.