Plant problems

Why Are My Catapodium Leaves Curling?

Q: How do I grow catapodium rigidum in a UK garden?

Catapodium rigidum (fern grass) is a small, delicate, annual grass that can be grown in a UK garden in a specialist wall or rock garden setting, or as an ornamental grass component of a dry, sunny, well-drained naturalistic or Mediterranean-style planting. It is one of the most diminutive and intricately structured grasses available for such settings and is particularly appropriate for planting in the joints and crevices of old stone walls or at the edge of a dry stone path. Sowing: surface sow fine seed in autumn (September to October) directly into the intended position, or into pots of dry, gritty, well-drained compost; the seed requires no cold stratification and germinates readily in autumn after fresh collection; stored seed retains viability for one to two years but is best fresh; press lightly into the surface and do not cover as the fine seed needs light for best germination. Position: an open, fully sunny, very well-drained or freely draining position in full sun; the base of an old stone or brick wall facing south or west, a dry stone retaining wall face, a rock garden crevice, or the sunny edge of a chalk or gravel path; catapodium is adapted to the driest, sunniest, most inhospitable positions in the garden and does not compete well with other vegetation; it is best grown in open, sparse, low-competition conditions. Soil: thin, dry, calcareous or neutral, freely draining substrate; the plant grows in wall mortar, chalky rubble, sandy path grit, and thin, rocky soils; it does not require fertile, organic-rich soil and is actually disadvantaged by rich, moist conditions where it is outcompeted by more vigorous plants. Self-seeding: once established in suitable open, dry conditions, catapodium self-seeds freely and can maintain itself from year to year in a wall or rock garden position; allow the plants to ripen fully and shed seed before removing the dried stems.

Q: What is the difference between catapodium rigidum and catapodium marinum?

Catapodium rigidum (fern grass, rigid fern grass, wall fern grass, syn. Desmazeria rigida) and Catapodium marinum (sea fern grass, sea hard grass, syn. Desmazeria marina) are two closely related annual grass species in the UK that share the same distinctive rigid, branching, fern-like panicle character but differ significantly in habitat, coastal versus inland distribution, and the character of their spikelets and panicle: Habitat: Catapodium rigidum is the more widespread and common species; it grows on dry walls, rocky ground, chalk grassland, path edges, and dry, open, disturbed ground throughout England and Wales; it is primarily an inland and lowland species although it also grows on sea cliffs and coastal outcrops; Catapodium marinum is a strictly coastal species in the UK, found on coastal paths, sea walls, cliff-tops, dune slacks, upper saltmarsh, and the open, dry, saline or spray-affected ground of the coastal zone; it does not occur inland. Panicle character: the panicle branches of Catapodium marinum tend to be somewhat less stiffly rigid and more rounded in cross-section than those of C. rigidum; the overall panicle of C. marinum tends to be more one-sided (distichous, arranged in a comb-like form along the stem) than the more openly branching panicle of C. rigidum; the spikelets of C. marinum tend to be somewhat broader and more rounded. Salinity tolerance: Catapodium marinum is salt-tolerant and is found in slightly saline to salt-spray-affected coastal habitats; Catapodium rigidum is not a specialist of saline conditions.

Q: What other small annual grasses grow on UK walls?

Old stone and brick walls in the UK support a fascinating and often overlooked community of small annual grasses and associated plants that specialise in the thin, freely draining, calcareous or neutral substrate of wall mortar, crevices, and wall tops. The most characteristic small annual grasses of UK walls include: Catapodium rigidum (fern grass): the most characteristic wall grass; stiff, fern-like, branching panicle; dry, sunny walls and rocky outcrops throughout England and Wales. Poa compressa (flattened meadow grass): a slightly larger, rhizomatous perennial grass of dry, hot walls and rocky places; distinctively flattened (compressed) stems; blue-green leaves; very drought-tolerant; common on urban walls throughout the UK. Poa annua (annual meadow grass): ubiquitous annual of pavement cracks, wall bases, and open disturbed ground; tiny, neat tufts with an open, triangular panicle; found in the sheltered lower zones of walls and at the base. Cerastium spp. (mouse-ears): not grasses but very commonly associated with the wall-top and wall-crevice community alongside the small grasses. Festuca ovina and Festuca rubra (sheep's fescue, red fescue): fine-leaved perennial fescues on drier, less disturbed wall tops and mortared crevices, particularly in upland and northern UK. Mibora minima (early sand grass): one of the smallest UK native grasses; a tiny annual of sandy and rocky ground in Wales and south-west England; produces its flower spike in February to April (very early for a grass); rare but occasionally found on rocky outcrops and sandy coastal banks. Veronica arvensis, Arabidopsis thaliana, Saxifraga tridactylites (rue-leaved saxifrage): characteristic associated annual wildflowers of the same wall-top habitat as the small annual grasses.

Catapodium rigidum (fern grass, rigid fern grass) is a small, wiry, annual grass of old walls, dry chalk grassland, rocky outcrops, and sunny path edges throughout England and Wales. One of the most characteristic grasses of the UK wall flora, distinguished by its stiff, fern-like, branching panicle. Leaves curl and brown from drought in its thin, freely draining habitats, summer heat triggering premature ripening, or the natural completion of the very short annual lifecycle by June to July.

Drought in thin, freely draining habitats

Despite growing in the driest wall, rock, and path-edge habitats in the UK, catapodium has a fine, shallow annual root system; in a prolonged or severe dry spell the wiry leaves curl and brown at the tips before the whole plant ripens prematurely. The curling is less pronounced than in softer-leaved grasses because the leaves are narrow and wiry, but tip browning and premature yellowing in drought are clearly visible on close inspection.

What to do

In a specialist wall or rock garden where catapodium is grown deliberately, a very light watering in extreme drought extends the active growth period and delays premature ripening; however, the plant is so well-adapted to drought conditions that overwatering is far more damaging than underwatering; water only once, deeply, in a sustained drought and allow the substrate to dry completely between waterings. The best approach is to allow catapodium to self-seed in an appropriate dry, sunny position and let the population time its lifecycle according to natural rainfall conditions each year.

Early summer heat and premature ripening

A cool-season annual, catapodium ripens earlier in a hot UK spring or early summer; in temperatures consistently above 22 to 25°C the plant ripens very quickly, the stiff, branched panicle turns from green to a rigid straw-coloured structure rapidly, and the whole plant dries while still quite small. Most noticeable on south-facing, sun-heated walls and dry, exposed, south-facing rocky habitats where temperatures are highest.

What to do

Accept that catapodium's main ornamental period is spring (March to May) in the UK and that it dries and dies by June to July regardless of conditions; its value is as a spring-season annual element in a wall or rock garden, not as a summer plant. In a very hot year, the dried straw-coloured panicles that persist on the wall through summer have their own architectural, structural interest; the rigid, branching dried panicle is attractive in its own right as a permanent structural feature of the wall face through summer and autumn.

Normal annual lifecycle completion

Catapodium germinates in autumn or early spring, grows as a tiny rosette through winter, flowers from April to June, and dies after setting seed by June to July. The whole above-ground growth browns, stiffens, and dries as the plant completes its annual lifecycle; the rigid, straw-coloured, fern-like dried panicle persists on walls and rocks through summer as a structural feature of the wall flora. This is entirely normal lifecycle completion.

What to do

Allow the plants to ripen fully and shed seed before removing any dried stems; catapodium self-seeds freely in suitable open, dry conditions and maintains itself from year to year in a wall or rock garden without intervention if shed seed is allowed to reach suitable open substrate. The very fine seed falls close to the parent plant and germinates in the same open, sunny, dry crevice or wall joint in autumn; no deliberate seed collection or sowing is needed once established in a suitable position.

Frequently asked questions

Why are my catapodium leaves curling?

Catapodium leaves curl most commonly because of drought in thin, freely draining habitats (fine, shallow annual roots; wiry leaves curl and tip-brown in prolonged dry spells; water once, deeply, in extreme drought only; overwatering far more damaging than underwatering; best left to time its lifecycle according to natural rainfall), early summer heat and premature ripening (cool-season annual; hot spring conditions above 22 to 25°C trigger rapid ripening; panicle turns straw-coloured very quickly on south-facing, sun-heated walls; accept spring as its main ornamental period; dried panicles have structural interest through summer), or normal annual lifecycle completion (flowers April to June; dies after seed set by June to July; dried panicles persist through summer; allow full ripening and seed shed before removing; self-seeds freely in open, dry, sunny crevices; no intervention needed once established). Extremely low-maintenance in the right dry, sunny position.

How do I grow catapodium rigidum in a UK garden?

Surface sow fine seed in autumn directly into intended position or into pots of dry, gritty compost; do not cover (needs light for germination). Open, fully sunny, very well-drained position in full sun: south or west-facing wall base, dry stone wall face, rock garden crevice, chalk or gravel path edge. Thin, dry, calcareous or neutral, freely draining substrate; wall mortar, chalky rubble, sandy grit; not fertile, moist soil (disadvantaged by rich conditions; outcompeted by more vigorous plants). Self-seeds freely in suitable open, dry conditions; maintain itself year to year without intervention; allow full ripening and seed shed before removing dried stems.

What is the difference between catapodium rigidum and catapodium marinum?

C. rigidum (fern grass): more widespread; dry walls, rocky ground, chalk grassland, path edges throughout England and Wales; primarily inland and lowland though also on sea cliffs. C. marinum (sea fern grass): strictly coastal; coastal paths, sea walls, cliff-tops, dune slacks, upper saltmarsh; not found inland; salt-tolerant. Panicle difference: C. marinum tends to be more one-sided (distichous, comb-like) and the spikelets are somewhat broader and more rounded than the more openly branching panicle of C. rigidum. Both distinguished from other UK grasses by the stiff, rigid, fern-like branching panicle character.

What other small annual grasses grow on UK walls?

Catapodium rigidum (fern grass): most characteristic UK wall grass; stiff fern-like panicle; throughout England and Wales. Poa compressa (flattened meadow grass): slightly larger rhizomatous perennial; compressed stems; blue-green leaves; drought-tolerant; common on urban walls. Poa annua (annual meadow grass): ubiquitous; wall bases and crevices; tiny tufts; open triangular panicle. Festuca ovina, F. rubra: fine-leaved perennial fescues on drier wall tops and crevices. Mibora minima (early sand grass): one of the UK's smallest native grasses; tiny annual of sandy and rocky ground in Wales and south-west England; flowers February to April; rare. Associated annual wildflowers: Saxifraga tridactylites (rue-leaved saxifrage), Arabidopsis thaliana, Veronica arvensis.