Why Are My Corynephorus Leaves Curling?
Corynephorus canescens (grey hair grass, clubawn grass) is a nationally rare, Schedule 8 protected, UK native grass of open, acid, dry, sandy heathland in East Anglia and a few coastal dune sites. One of the most distinctive UK grasses, forming dense silvery-grey cushions with fine bristle-like leaves and a distinctive dumbbell-shaped awn. Leaves curl and brown from drought in its preferred open sand, waterlogging in wet or clay soils, or competition closing in on its bare-sand habitat.
Drought in dry sandy habitat
Genuinely drought-adapted, corynephorus is more drought-tolerant than almost any other UK native grass; however, in a prolonged or severe drought the leaf tips brown and the silvery-grey colour of the tuft becomes duller and more yellowed. The characteristic silvery colour is most vivid in actively growing, well-hydrated plants; drought reduces the reflective quality of the fine, hairy leaf surface. Most cases of poor performance in cultivation result from waterlogging rather than drought.
What to do
- No supplemental watering is needed in most UK conditions once established; overwatering is far more dangerous than underwatering for corynephorus in a UK garden. If growing in a container or trough that dries out very rapidly in a hot summer, a single deep watering in the most extreme drought is acceptable; otherwise allow the extremely freely draining substrate to manage itself. In a garden context, if the plant is browning in what seems to be drought, check drainage first: waterlogging browning is far more common in UK gardens than drought browning.
Waterlogging and poorly drained soils
The primary cause of corynephorus failure in UK gardens. One of the most waterlogging-intolerant of all UK native grasses; even brief waterlogging in a heavy clay or poorly draining soil is fatal; the fine roots require a very freely draining, open, aerated, acid sandy substrate; anaerobic waterlogged conditions cause rapid yellowing from the base upward, followed by tuft collapse and plant death.
What to do
- Plant only in extremely freely draining, acid, nutrient-poor, sandy or gravelly soil; a raised bed or trough filled with two-thirds horticultural grit to one-third acid compost (ericaceous, peat-free) is the most reliable UK garden approach; pH 4.5 to 6.0; no lime or alkaline material. If a planted corynephorus begins yellowing from the base, check the drainage immediately; if the substrate is even slightly wet or compacted, remove the plant, allow it to dry in a freely draining tray of dry grit, improve the drainage of the planting position radically, and replant.
Competition and sward closure
Corynephorus requires open, bare, or sparsely vegetated sand with very low competition; even low-growing prostrate plants competing for light and moisture at the base of the tufts weaken it. Without the maintaining factors of sand instability, rabbit grazing, or very low soil fertility, successional vegetation development can eliminate corynephorus from a garden or conservation site within five to ten years.
What to do
- Keep the area around corynephorus very open and free of competing vegetation; hand-remove any seedling weeds, annual grasses, or prostrate mat-formers promptly; a mulch of very coarse horticultural grit around the base of the tufts helps suppress competing seedlings and maintains the open, dry-soil conditions. At conservation sites in Suffolk, maintaining rabbit grazing and periodic removal of encroaching scrub and bracken are the most important management actions for the long-term persistence of corynephorus populations.
Frequently asked questions
Why are my corynephorus leaves curling?
Corynephorus leaves curl most commonly because of waterlogging and poorly drained soils (primary cause of failure in UK gardens; one of the most waterlogging-intolerant UK native grasses; rapid yellowing from base in waterlogged clay; plant in extremely freely draining acid sandy grit; raised bed or trough with two-thirds horticultural grit to one-third ericaceous compost; pH 4.5 to 6.0; no lime), drought in dry sandy habitat (genuinely drought-adapted; most drought-tolerant of UK native grasses; leaf tips brown and silvery colour dulls in severe drought; no supplemental watering needed in most UK conditions; check drainage before assuming drought is the cause), or competition and sward closure (requires open bare sand; even low-growing prostrate competitors weaken it; hand-remove all competing seedlings; mulch with coarse grit; maintain rabbit grazing and scrub control at conservation sites). Drainage trumps everything else in a UK garden context.
Where does corynephorus canescens grow in the UK?
Nationally rare; primarily confined to Suffolk Sandlings (main UK stronghold on open acid inland sandy heathland from Ipswich northward to Lowestoft), Norfolk (a few sites on inland sandy heathland and blown sand), and very few coastal dune sites in East Anglia and occasionally Wales. Protected under Schedule 8 of the Wildlife and Countryside Act 1981 in England and Wales (may not be picked, uprooted, or intentionally destroyed). UK Biodiversity Action Plan priority species. Threats: scrub encroachment; bracken spread; reduction of rabbit grazing; Rhododendron ponticum invasion; lack of site management. Much more widespread in continental Europe from Portugal through France, Low Countries, Germany, and Scandinavia.
How do I grow corynephorus canescens in a UK garden?
Source only from specialist cultivated nursery stock (never from the wild; Schedule 8 protected). Soil: extremely freely draining, acid, nutrient-poor, sandy or gravelly; raised bed or trough with two-thirds horticultural grit and one-third peat-free ericaceous compost; pH 4.5 to 6.0; no lime or alkaline material. Position: full sun; open, exposed; sheltered, shaded, or north-facing positions unsuitable. Watering: water only to establish; overwatering is the primary risk in UK conditions; allow soil to dry completely between waterings; do not water in winter. Competition: keep surrounding area very open and free of competing vegetation; mulch with coarse grit. Overwatering and drainage failure are the main reasons corynephorus fails in UK gardens.
What makes corynephorus canescens so distinctive among UK grasses?
Grey-silver colour: soft silvery-grey to blue-grey colouration unlike any other common UK grass; from a dense covering of very short fine hairs on leaf surface and sheath that reflect light strongly; most vivid and bright in active spring growth; dulls in drought or winter dormancy. Leaf form: very narrow, bristle-like, tightly in-rolled (setaceous); dense, wiry, fine-textured, cushion-forming character; architecturally very striking. Dumbbell awn: bent abruptly at midpoint; upper half club-shaped or distinctively swollen at the tip; unique among UK grasses; visible with a hand lens; the most reliable microscopic identification character. Panicle: fine-branched, open, airy; greyish-purple to silvery-violet colouration; very attractive; produced June to July. Cushion form: dense, dome-shaped or rounded cushions of fine silvery-grey bristle-like leaves; genuinely beautiful in full active growth.