Tips for Planting a Rock Garden
Traditionally, rock gardens have served as self-contained areas in which gardeners can grow the sort of plants normally found in high, mountainous, alpine habitats. For this reason, they are purposely constructed from rocks and stones in an attempt to mimic the bare outcrops, scree slopes, ledges, and crevices found at high altitudes. Most of the plants that thrive in rock gardens are small and compact, and tend to be tough and drought-resistant. Many of them flower profusely, in a range of brilliant colors.
Contemporary garden design, however, has broadened the definition of the term “rock garden.” Drawing inspiration from Mediterranean and desert landscapes, and employing lots of hard surfaces such as paving, pebbles, river stones, and gravel, modern rock gardens are as likely to feature cacti and succulents as true alpines.
Creating a Rock Garden
The best site for an alpine rock garden is an open, sunny, south-facing slope. Almost all rock plants grow best with lots of light and in well-drained soil. They don’t do well where the soil is damp and heavy, or where there are overhanging trees. If you’re constructing a rock garden from scratch, first lay a foundation of coarse rubble, such as broken bricks, to create a gradient or form a mound. Cover it with inverted sod or a sheet of polypropylene punctured to let water drain through freely.
Place your rocks on top, positioning the largest ones first. Salvaged or second-hand stones are best—particularly sandstone, limestone, or tufa. Aim for a natural-looking mix of bare outcrops, miniature ravines and gullies, and plenty of crevices for planting. Infill the stones with good garden soil, and then spread a top layer of specially prepared soil comprising equal parts loam, garden compost or leafmold, and sharp sand or grit. You may want to leave some areas as scree beds, covering them with a mix of coarse grit, gravel, or stone chips.
Choosing Plants for Rock Gardens
Some rock-garden plants are true “alpines,” and some aren’t. Those that are actually come from alpine regions, where they grow above the tree line, having evolved to withstand the extreme weather conditions found at high altitudes. Most are dwarf or low-growing and hug the ground to avoid buffeting from strong winds. Their leaves tend to be small, fleshy, and often covered by woolly hairs in order to help them retain moisture that would otherwise evaporate in hot sun or constant wind.
Nonalpines include dwarf trees and shrubs, plants that originate on cliffs and shores in coastal areas, a wide range of miniature bulbs, and even cacti and succulents. In general, all share the same dislike of being waterlogged and a preference for free-draining, moderately fertile soils.