UK compost
What compost for split rock in the UK?
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More about split rock in the UK
Which compost split rock needs
For split rock the mix to buy is peat-free multipurpose compost cut roughly half-and-half with horticultural grit or perlite. Mostly inorganic — about 70-80% grit (pumice, coarse sand, or perlite) to 20-30% potting compost; a 3:1 blend of pumice to succulent mix also works. Use a deep, narrow pot with a drainage hole to suit the long taproot and prevent standing moisture.In British garden centres the bagged growing medium is sold simply as “compost” (multipurpose, ericaceous, or loam-based John Innes), which is a different thing from the rotted garden “compost” you make in a heap — for a pot you want the bagged kind.
Peat-free compost
Buy peat-free. The sale of peat compost to home gardeners is being phased out across the UK, and the RHS recommends peat-free on environmental grounds. A good peat-free multipurpose grows split rock perfectly well; the one habit to change is watering — peat-free dries faster at the surface while still moist below, so check by feel a knuckle deep rather than trusting the look of the top.
Ericaceous or multipurpose?
Split Rock does not want a rich, water-holding compost — it wants sharp drainage. Cut peat-free multipurpose roughly half-and-half with horticultural grit, sharp sand or perlite, and always pot into a container with drainage holes. A "cactus and succulent" bagged mix is a ready-made shortcut.
For the full recipe, pH and drainage detail (US wording), see the split rock soil & potting-mix guide.
Compost for Split Rock in the UK — frequently asked questions
What compost should I use for split rock in the UK?
Use peat-free multipurpose compost cut roughly half-and-half with horticultural grit or perlite. Mostly inorganic — about 70-80% grit (pumice, coarse sand, or perlite) to 20-30% potting compost; a 3:1 blend of pumice to succulent mix also works. Use a deep, narrow pot with a drainage hole to suit the long taproot and prevent standing moisture. In UK garden centres this is sold simply as "compost" — the bagged growing medium, not garden-made leaf-mould — so match the description above rather than a brand.
Can I use ordinary multipurpose compost for split rock?
Not on its own — multipurpose compost holds too much water for split rock and will rot the roots. Cut it roughly 50:50 with horticultural grit, sharp sand or perlite so it drains fast.
Should the compost be peat-free?
Yes. Sales of peat compost to home gardeners are being phased out in the UK, and the RHS recommends peat-free for environmental reasons. Modern peat-free multipurpose composts grow split rock perfectly well — they dry a little faster at the surface, so check moisture by feel rather than by the look of the top.
Does split rock need grit or perlite added?
Yes — split rock must have sharp drainage. Add about one part horticultural grit or perlite to one part compost, and always use a pot with drainage holes.
What pot and drainage does split rock need?
Always a pot with drainage holes. Extremely free-draining gritty mineral mix. Stand it on a saucer, empty any water that collects after watering, and never leave the pot sitting in a full outer cover — waterlogged compost in a cool UK room is the commonest cause of root rot.
More split rock care
See the full split rock care guide, its UK watering and UK hardiness.