How to Contain Decorative Rock With Borders

Select perennial plants that stay low to the ground and that will complement your rock garden with their foliage and colors. You want your rock garden to be accented by the border, not obscured.

Choose colorful, sun-loving perennials that thrive in neutral to alkaline soil for the border of your rock garden. Rock cress--which spreads to 12 inches across and exhibits white, pink and lilac flowers in the spring-- and Basket of Gold, another spring bloomer with bright yellow flowers and yellow and gray foliage, are good choices, as is soapwort, which displays intense pink flowers in early summer. Sedum, also known as stone crop, blossoms in yellow, pink or white, and is another natural for bordering rock gardens, while hardy, cheerful phlox--which displays pink or magenta flowers as early as March--will also thrive in rock garden borders. Finally, hens and chicks, which have sage-green foliage and intriguing, layered rosette shapes, spread easily and flourish in rocky soil.

Choose perennials that require--or at least tolerate--partial shade if you have large rocks in your garden that are big enough to create shadows over the border. Windflowers, with delicate blue to purple blossoms, won't exceed a foot in height, and bloom from April to May. English daisies, in red, white, or salmon pink, and saxifrage, which blooms in pink, yellow, and snowy white, also do well in partial shade. Finally, to introduce a note of bright orange or yellow, plant Siberian wallflower.

Before digging the edging, place the plants in their pots around the rock garden to determine what looks best to you, remembering to allow for shade and sun requirements. Remember also that they will spread out, so the final result will be much more luxuriant.

Edge the rock garden by beginning about 1.5 feet from where your garden ends, and dig in at a slight angle with your shovel, breaking up dirt clods as you go. Continue until you have created an angled trench around your rock garden. It should be a uniform depth, about as deep as the root balls of your perennial flowers, and at least twice around as wide. Amend the soil with organic compost to provide nutrients.

Set your plants in the trench and backfill, then tamp soil and water the border thoroughly. Apply an inch and a half of mulch to protect the roots and conserve moisture.

Border your newly planted perennials with small edging stones that are consistent with those in the rock garden to create an effect that is unified, yet still organic. This also helps keep the mulch in place and prevents grass and weeds from creeping into the border.