If you have a group of rocks as a landscape feature in your yard, you can show it off with appropriate plantings. Here are some ideas for what to plant, plus tips for planting near the rocks:
Choose plantings that show off the group of rocks. Plant low-growing plants like alyssum, bleeding hearts (Dicentra), catmints (Nepeta), stonecrop (Sedum) and hens and chicks (Sempervivum), Corsican mint, lungworts (Pulmonaria) and other pretty little plants that will splash the group with bits of color but stay low enough that the rocks will remain visible. If you plant shrubs behind the group of rocks, use dark green evergreens like false cypress (Chamaecyparis obtusa ‘Nana Gracilis’) and interesting deciduous shrubs like Harry Lauder’s walking stick (Corylus avellana ‘Contorta’) with its twisty branches. Redtwig dogwood’s (Cornus stolonifera) red branches will look good in winter when snow adorns the rocks, if you live in a snowy area.
When siting rocks on a slope, make planting pockets. If you have a slope or berm, you can make very attractive arrangements of rocks that provide spaces for alpines or other small or cascading plants. Let’s say you’ve installed two large rocks about two feet apart at the base of a slope. If you then fill the space between them with a smaller rock that’s slightly lower, you can fill the space behind the smaller rock with good garden soil and set in an alpine or other small plant. You can stagger rocks this way up the slope, making small, level planting areas behind them as you go. The effect, when planted with alpines, is beautiful. Avoid the thought of topping the slope or berm with a dominant rock. It’s much better to choose a plant with a horizontal habit. For a large slope or berm, Viburnum plicatum tomentosum ‘Mariesii’ comes to mind.