UK compost
What compost for penstemon 'sour grapes' in the UK?
Penstemon 'Sour Grapes'
More about penstemon 'sour grapes' in the UK
Which compost penstemon 'sour grapes' needs
For penstemon 'sour grapes' the mix to buy is peat-free multipurpose compost cut roughly half-and-half with horticultural grit or perlite. Neutral to slightly alkaline pH suits it best. Winter waterlogging is fatal, so add grit to heavy clay and avoid soils that hold cold water.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 penstemon 'sour grapes' 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?
Penstemon 'Sour Grapes' 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 penstemon 'sour grapes' soil & potting-mix guide.
Compost for Penstemon 'Sour Grapes' in the UK — frequently asked questions
What compost should I use for penstemon 'sour grapes' in the UK?
Use peat-free multipurpose compost cut roughly half-and-half with horticultural grit or perlite. Neutral to slightly alkaline pH suits it best. Winter waterlogging is fatal, so add grit to heavy clay and avoid soils that hold cold water. 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 penstemon 'sour grapes'?
Not on its own — multipurpose compost holds too much water for penstemon 'sour grapes' 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 penstemon 'sour grapes' perfectly well — they dry a little faster at the surface, so check moisture by feel rather than by the look of the top.
Does penstemon 'sour grapes' need grit or perlite added?
Yes — penstemon 'sour grapes' 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 penstemon 'sour grapes' need?
Always a pot with drainage holes. Fertile, free-draining loam that stays moist but not wet. 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 penstemon 'sour grapes' care
See the full penstemon 'sour grapes' care guide, its UK watering and UK hardiness.