UK compost
What compost for snake's head iris in the UK?
Hermodactylus tuberosus
More about snake's head iris in the UK
Which compost snake's head iris needs
For snake's head iris the mix to buy is peat-free multipurpose compost cut roughly half-and-half with horticultural grit or perlite. Prefers alkaline to neutral pH on chalk, limestone, or gritty loam; add lime to acid soils and improve drainage with coarse grit before planting the finger-like tubers.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 snake's head iris 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?
Snake's Head Iris 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 snake's head iris soil & potting-mix guide.
Compost for Snake's Head Iris in the UK — frequently asked questions
What compost should I use for snake's head iris in the UK?
Use peat-free multipurpose compost cut roughly half-and-half with horticultural grit or perlite. Prefers alkaline to neutral pH on chalk, limestone, or gritty loam; add lime to acid soils and improve drainage with coarse grit before planting the finger-like tubers. 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 snake's head iris?
Not on its own — multipurpose compost holds too much water for snake's head iris 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 snake's head iris perfectly well — they dry a little faster at the surface, so check moisture by feel rather than by the look of the top.
Does snake's head iris need grit or perlite added?
Yes — snake's head iris 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 snake's head iris need?
Always a pot with drainage holes. Alkaline, sharply drained gritty loam or chalk. 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 snake's head iris care
See the full snake's head iris care guide, its UK watering and UK hardiness.