How-to Guide
How to Make a Rock Garden and Grow Alpines
The short answer
Build for drainage first: lay a base about 15cm (6in) deep of coarse rubble, broken brick, stone, or pea shingle, then plant into a gritty, low-fertility mix - one part loam, one part horticultural grit, one part leafmould or coir, or a soil-based mix such as peat-free John Innes No1 with up to 30% added grit by volume - and finish with a grit or gravel top-dressing.
Put the rock garden in the most open, sunny position you have, away from overhanging trees and their roots, and plant in spring so alpines establish before winter. Their real enemy is winter wet sitting around the crown, not cold, which is why the fast-draining media matters so much.
Drainage is the whole game
Alpines evolved in thin mountain soils that drain almost instantly, so a rock garden has to mimic that. The RHS recommends building a base 15cm (6in) deep of coarse rubble, broken bricks, stone, ballast, or pea shingle, and separating that from the layer above with inverted turves, perforated polythene, or permeable landscape fabric so the drainage layer does not silt up.
The planting mix should be gritty and low in fertility: one part loam (ideally sterilised, though garden soil will do), one part horticultural grit, and one part leafmould or coir. A soil-based potting medium such as peat-free John Innes No1 with added grit up to 30% by volume also works. Rich, moisture-holding soil makes alpines soft and short-lived.
Position and planting
Choose the most open position you have, away from overhanging trees or tree roots, where plants receive sun for the greater part of the day. If a fully open spot is not possible, the RHS advises that fewer hours of direct sun per day is better than a whole day of light shade.
Spring is the optimum time to plant, both because the widest range of alpines is available then and because it gives plants a full growing season to establish before winter. After planting, top-dress the surface with gravel or grit - this keeps the crown of each plant dry, sets off the plants visually, and suppresses weeds.
Why winter wet, not cold, is the risk
Alpines are extremely cold-hardy - in the wild they spend winter under insulating snow. What they cannot tolerate is sitting in cold, wet soil, which rots the crown and roots. The RHS names winter wet as the challenge and enemy of rock plants.
Everything about rock-garden construction - the rubble base, the gritty mix, the grit collar around each plant - is aimed at keeping water moving away from the plant rather than pooling around it. In very wet climates, a pane of glass propped over choice alpines in winter, or growing them in raised troughs, gives extra protection.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- Royal Horticultural Society (RHS) - Create a Rock Garden with Alpines — Specifies a 15cm (6in) coarse-rubble drainage base, a gritty low-fertility mix (one part loam / one part grit / one part leafmould or coir, or peat-free John Innes No1 with up to 30% grit by volume), a grit/gravel top-dressing, the most open sunny position away from trees, spring planting, and identifies winter wet as the main killer of alpines.