A rock garden is a garden built around stones, with plants that thrive in the gaps, crevices and pockets between them. It is one of the oldest garden styles, inspired by mountain landscapes, and it suits alpines, succulents and other plants that need sharp drainage and love sun. A well-built rock garden looks natural, needs little water, and is full of interest for most of the year, with small flowers appearing in every season.
Rock gardens suit slopes, awkward corners, sunny banks and small gardens, and they are a good use for stone that would otherwise be wasted. The key is to build the structure well — stones set firmly, soil that drains sharply, and plants chosen for the conditions — and then to leave the garden to settle and grow. If you are unsure which alpine plants suit your climate, check your local extension service for local recommendations.
Designing a rock garden
Design a rock garden to look like a natural outcrop, not like a pile of stones. Choose a sunny, well-drained spot — a slope is ideal, because it gives natural drainage and lets you see the plants from below, but a flat site can be built up into a low mound. Sketch the shape, and think about scale: a rock garden should be big enough to hold several groups of plants, but small enough to maintain. Use local stone if you can, because it will look at home and it is cheaper to transport. Mix stone sizes, with a few large boulders as anchors and smaller stones filling in, and bury each stone by at least a third so it looks settled, not perched. Leave planting pockets between stones, with good soil in them, and leave paths or stepping stones so you can reach plants to weed and tend them without standing on the rockery. Our garden design basics guide helps with the overall plan.
Choosing and placing stones
Stone is the structure of a rock garden, so choose it carefully. Sandstone, limestone and granite all work, but avoid soft stone that crumbles, and avoid stone with sharp, fresh edges that looks quarried rather than natural. Use one type of stone throughout, because mixed types look messy. Place the largest stones first, setting them firmly into the ground with their longest side horizontal, and tilt them slightly back into the slope so rain runs into the planting pockets rather than off the front. Fill behind them with a free-draining soil mix — roughly equal parts topsoil, grit and compost — and firm it in. Do not use ordinary garden soil on its own, because it holds too much water and will rot alpines. Work from the bottom of the slope upwards, and stand back often to check the shape. A rock garden built well will look good even before it is planted, and it will look better every year as plants settle in and soften the stones.
Soil and drainage for alpines
Drainage is everything in a rock garden. Alpines evolved in mountains, where water drains away instantly and roots never sit wet, especially in winter. Use a gritty mix — topsoil, coarse grit and compost — and top-dress around plants with grit, which keeps the crown dry, stops soil splashing onto leaves, and suppresses weeds. Do not use rich compost or manure, because alpines prefer poor soil and will grow soft and leggy in rich ground. Test the soil pH if you plan to grow lime-hating alpines such as heathers — our soil pH testing guide explains how — and choose plants to match the pH you have rather than trying to change it. Water new plants in, then water sparingly: most rock garden plants need little water once established, and over-watering is more likely to kill them than drought. In winter, the danger is wet, not cold, so make sure water drains away freely and does not collect in pockets.
Best plants for a rock garden
Choose plants that are small, tough and happy in sharp drainage. Alpines such as saxifrage, aubrieta, arabis, phlox, campanula and sempervivum are classic rock garden plants, flowering in spring and early summer in a carpet of colour. Sedums and stonecrops store water in their leaves and cope with drought and sun. Thyme, especially creeping thyme, fills gaps and smells wonderful — see growing thyme. Dwarf bulbs such as crocus, miniature daffodils and grape hyacinths flower early and then disappear, leaving room for summer plants. Small shrubs such as dwarf conifers, heathers and rock roses give structure all year. Avoid large, vigorous plants that will swamp their neighbours, and avoid thirsty plants that need rich, moist soil. Plant in drifts of the same species, because a mass of one alpine looks better than a single plant of many kinds, and leave room for plants to spread — a rock garden that is planted too tightly will be a tangle within a year.
Planting and maintaining a rock garden
Plant in spring or autumn, when the soil is moist and the weather is kind. Make a hole in the planting pocket, set the plant at the same depth it was in its pot, firm the gritty mix around it, and top-dress with grit. Water in, then leave it — most alpines need little aftercare. Weed little and often, because weeds in a rock garden are hard to remove once they root between stones, and pull them while they are small. Remove dead leaves and flowers regularly, and cut back plants that are swamping their neighbours. Divide and replant alpines that outgrow their space every few years, and replace any that die — a gap in a rock garden is easy to fill, and a new plant will settle quickly. Feed sparingly, if at all: a light dressing of compost in spring is enough, and too much feed produces soft growth. Check stones after frost, and reset any that have moved. A rock garden needs little work, but the work it needs is regular and gentle.
Rock gardens in shade and small spaces
Rock gardens are usually sunny, but a shady rock garden can work too, with the right plants. In part shade, grow ferns, hostas in miniature, saxifrage, primulas, hellebores and shade-tolerant sedums, and use pale stones to brighten the shade. Avoid deep shade, where few alpines will flower. In a small garden, a rock garden can be as small as a single large trough or a raised bed filled with gritty mix and planted with alpines — a trough garden is a classic, and it can sit on a patio or a balcony. Use a stone or terracotta trough, drill drainage holes, fill it with gritty mix, and plant it with small alpines and a dwarf conifer. A trough garden needs watering more often than a rock garden in the ground, because it dries out fast, but it is easy to tend and it looks beautiful. Even a single stone with a saxifrage growing in a crevice can be a tiny rock garden.
Common mistakes to avoid
The biggest mistake is using ordinary garden soil in a rock garden, which holds too much water and rots alpines, especially in winter. The second is perching stones on the surface instead of burying them, so they look like a pile of rubble and wobble when touched. The third is planting large, vigorous plants that swamp small alpines within a season. The fourth is over-watering and over-feeding, which produces soft growth that rots. The fifth is planting in deep shade and expecting sun-loving alpines to flower. The sixth is letting weeds take hold between stones, where they are hard to remove. Finally, do not build a rock garden in a hollow where water collects — it needs drainage above all, so choose a slope or a raised mound, and if your soil is heavy clay, build the rock garden up rather than digging it in. If alpines keep dying, check your local extension service for advice on soil and plant choices for your area.
Frequently asked questions
What soil should I use in a rock garden?
A free-draining, gritty mix — roughly equal parts topsoil, coarse grit and compost. Do not use ordinary garden soil on its own, and do not use rich manure. Top-dress around plants with grit to keep crowns dry and suppress weeds.
Can I build a rock garden on a flat site?
Yes — build it up into a low mound, so water drains away, or use a raised bed or a large trough. A flat rock garden that is not raised will hold water and rot alpines, especially in winter, so drainage is essential.
What are the easiest rock garden plants?
Aubrieta, saxifrage, sempervivum, sedum, creeping thyme, arabis and phlox are all easy, tough and free-flowering. Start with these, and add more unusual alpines once you are confident. Plant in drifts for the best effect.
How much water does a rock garden need?
Very little once plants are established. Water new plants in, water in long dry spells, and otherwise leave them alone. Over-watering is more likely to kill alpines than drought, especially in winter when wet roots rot.
Can I have a rock garden in shade?
A sunny spot is best, but a part-shaded rock garden can work with ferns, saxifrage, primulas, hellebores and shade-tolerant sedums. Avoid deep shade, and use pale stones to brighten the area. Sun-loving alpines will not flower well in shade.