UK compost
What compost for welsh onion in the UK?
Allium fistulosum
More about welsh onion in the UK
Which compost welsh onion needs
For welsh onion the mix to buy is peat-free multipurpose compost cut roughly half-and-half with horticultural grit or perlite. Loose, well-worked soil enriched with compost. Good drainage is essential to prevent crown and root rot; raised beds suit heavier clay sites.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 welsh onion 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?
Welsh Onion 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 welsh onion soil & potting-mix guide.
Compost for Welsh Onion in the UK — frequently asked questions
What compost should I use for welsh onion in the UK?
Use peat-free multipurpose compost cut roughly half-and-half with horticultural grit or perlite. Loose, well-worked soil enriched with compost. Good drainage is essential to prevent crown and root rot; raised beds suit heavier clay sites. 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 welsh onion?
Not on its own — multipurpose compost holds too much water for welsh onion 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 welsh onion perfectly well — they dry a little faster at the surface, so check moisture by feel rather than by the look of the top.
Does welsh onion need grit or perlite added?
Yes — welsh onion 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 welsh onion need?
Always a pot with drainage holes. Fertile, free-draining loam, pH 6.0-7.0. 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 welsh onion care
See the full welsh onion care guide, its UK watering and UK hardiness.