Plant problems

Why Are My Leersia Leaves Curling?

Q: How do I grow leersia oryzoides in a UK wildlife pond?

Leersia oryzoides (cut grass) can be grown in a UK garden wildlife pond or natural wet habitat as a native species of conservation value. It is a specialist plant of permanently wet, low-nutrient, open habitats and requires specific conditions to thrive. Water requirements: the roots and rhizomes must be in permanently saturated soil or very shallow standing water (up to 10 to 20 cm deep); the plant grows in the emergent zone at the very edge of still or slow-moving water; do not allow the root zone to dry at any point in the growing season. Light: full sun to very light shade; a minimum of five to six hours of direct sun per day; the most open, sunny pond margin position available gives the best growth and flowering; avoid heavy shade from overhanging trees. Soil: low-nutrient, wet, muddy, organic soil at the waterline; the plant is adapted to nutrient-poor wetland soils and does not perform well in nutrient-rich, eutrophic conditions or in the presence of vigorous, competitive wetland plants; it may be outcompeted by common reed (Phragmites), reed sweet grass (Glyceria maxima), or reed mace (Typha) in fertile, nutrient-rich water bodies. Establishment: can be established from divisions or pot-grown plants from a specialist native aquatic plant supplier; plant directly into the wet mud at the pond margin or in a planting basket submerged to just below or at the water surface; keep well watered and prevent drying during establishment; once established and spreading by rhizomes, the plant is self-maintaining in suitable conditions. Management: leersia spreads slowly by rhizomes and does not typically become invasive in a garden pond; it can be managed by removing excess growth from the pond margin; the hollow stems and tangle of rhizomes at the pond edge provide valuable habitat for insects, amphibians, and other aquatic wildlife.

Q: How is leersia related to rice?

Leersia oryzoides (cut grass, rice cutgrass) is closely related to cultivated rice (Oryza sativa) and wild rice species of the genus Oryza; both Leersia and Oryza are placed in the rice subfamily Ehrhartoideae (or Oryzoideae in some treatments) of the grass family (Poaceae), which is the subfamily containing the rice tribe and the major cultivated grain crop of more than half the world's population. The species epithet of Leersia oryzoides — 'oryzoides' — means 'rice-like' in botanical Latin, reflecting the botanical and visual resemblance between leersia and rice (Oryza): both are tall, emergent, semi-aquatic grasses of warm-temperate to subtropical wet habitats; both have similar leaf shape, similar flower structure, and both grow in shallow water or permanently wet, saturated soil. The key botanical features shared by Leersia and Oryza: both produce single-flowered spikelets with the palea and lemma strongly keeled and boat-shaped, compressed laterally; the spikelets lack the glumes (or have only very reduced glumes) that are prominent in most grass spikelets; the grains of Leersia (not commercially significant) superficially resemble a small, unpromising version of a rice grain. Leersia oryzoides is not related to the edible wild rice of North America and Canada, which is Zizania aquatica (a different genus, also in the Ehrhartoideae subfamily but in the wild rice tribe Zizanieae rather than the rice tribe Oryzeae). UK gardeners should be aware that despite its close relationship to rice, Leersia oryzoides does not produce edible grain and is valued as a native wildflower and habitat plant rather than as a food plant.

Leersia oryzoides (cut grass, rice cutgrass) is a UK native, rhizomatous, perennial grass of permanently wet pond and river margins, related to rice (Oryza sativa). Named for the sharp, backward-pointing silica teeth on the leaf edges that cut into bare skin. A rare and locally distributed native plant of conservation interest in the UK, primarily in southern England. Leaves curl and yellow from water level dropping, insufficient light, or late spring frost on emerging shoots.

Drought and water level dropping

Leersia oryzoides is an obligate wetland plant; its roots and rhizomes must be in permanently saturated soil or shallow standing water throughout the growing season. If the water level drops significantly in a dry UK summer, exposing the root zone, the narrow leaves curl from the margins and tips yellow within days. Leersia is much more sensitive to drying out than most waterside plants.

What to do

Maintain a permanently wet or submerged root zone throughout the growing season; top up the pond or water feature in dry spells to keep the root zone in standing water or permanently saturated mud. The ideal position is the emergent zone at the very edge of still or slow-moving water, with the roots in up to 10 to 20 cm of standing water or continuously saturated mud. Do not plant on a pond bank that dries out between rain events; leersia shows stress within days of water loss from the root zone.

Insufficient light

Found in open to lightly shaded wet habitats, leersia requires four to six hours of direct sun per day; in a heavily shaded pond margin shaded by overhanging trees, buildings, or shrubs, the plant produces weaker, paler, more widely spaced leaves and the characteristic nodding, narrow panicle of small, flat spikelets is sparse or absent. Leaves may curl and yellow in heavily shaded, wet positions from inadequate light energy for normal photosynthesis.

What to do

Plant in the most open, sunny, waterside position available; a south-facing or west-facing pond margin in full sun or very light dappled shade gives the best growth and flowering. Manage overhanging trees and shrubs around the pond margin to maintain open light conditions; the deterioration of leersia populations at many UK sites is partly attributed to the shading caused by scrub encroachment following the end of traditional pond management. In a wildlife garden, maintaining an open, sunny, unshaded pond margin is the most important management action for leersia.

Late spring frost damage

The young shoots emerge from the rhizomes in late spring (April to May) and are susceptible to late frost damage; a late frost in April or early May blackens, curls, and kills the soft emerging shoots. The plant is fully hardy in winter dormancy but the fresh spring growth emerging from the rhizomes at the water's edge is more vulnerable; damaged shoots are replaced by new growth from the rhizomes but the frosted early growth creates a temporarily untidy appearance.

What to do

In a frost-prone garden or in an exposed, low-lying, frost-pocket position, protect the emerging spring growth with horticultural fleece draped over the pond margin on nights when late frost is forecast; remove the fleece during the day. Alternatively, accept that late frost damage is temporary and cosmetic; the plant recovers and produces replacement growth that is typically unaffected. A sheltered pond position with some protection from late frosts reduces the frequency and severity of this problem.

Frequently asked questions

Why are my leersia leaves curling?

Leersia leaves curl most commonly because of drought and water level dropping (obligate wetland plant; roots must be in permanently saturated soil or up to 10 to 20 cm of standing water throughout the growing season; water level drop causes rapid leaf curl; top up pond in dry spells; do not plant on a bank that dries between rain events), insufficient light (requires four to six hours direct sun per day; shaded pond margin causes weak, pale, widely spaced leaves and sparse or absent flowering; manage overhanging trees; plant in the most open, sunny, waterside position available), or late spring frost on emerging shoots (young growth in April to May is frost-susceptible; protect with fleece on forecast frost nights; replacement growth from rhizomes is typically unaffected; cosmetic damage only). Permanently wet, open, sunny position is essential.

How do I grow leersia oryzoides in a UK wildlife pond?

Roots must be in permanently saturated soil or very shallow standing water (up to 10 to 20 cm deep) throughout the growing season. Full sun to very light shade; minimum five to six hours direct sun per day. Low-nutrient, wet, muddy, organic soil at the waterline; poor performer in nutrient-rich, eutrophic conditions; outcompeted by common reed, glyceria, and typha in fertile water. Establish from divisions or pot-grown plants from a specialist native aquatic plant supplier; plant directly into wet mud at the pond margin or in a planting basket at or just below water surface. Spreads slowly by rhizomes; manageable in garden ponds. Stems and rhizomes provide habitat for insects, amphibians, and aquatic wildlife; noted food plant for the water rail.

How is leersia related to rice?

Closely related to cultivated rice (Oryza sativa); both Leersia and Oryza are in the rice subfamily Ehrhartoideae of the grass family (Poaceae). The species epithet 'oryzoides' means 'rice-like' in botanical Latin. Shared botanical features: single-flowered spikelets with strongly keeled, boat-shaped lemma and palea; reduced or absent glumes; semi-aquatic habit. Not related to North American wild rice (Zizania aquatica), which is in a different tribe (Zizanieae) within the same subfamily. Leersia oryzoides does not produce edible grain and is valued as a native wildflower and habitat plant, not a food plant.

Is leersia oryzoides rare in the UK and why?

Scarce and locally distributed; primarily southern England; classified as near threatened or vulnerable in UK plant red lists. Main causes of rarity: habitat loss (drainage and canalisation of rivers and wetlands; many former pond systems drained or degraded); eutrophication (agricultural run-off, sewage, and urban drainage enriching water bodies with nutrients; vigorous competitive plants displace leersia in nutrient-rich conditions); shading (abandonment of traditional pond management; scrub encroachment and overhanging trees shade pond margins; succession from open sunny wetland to carr woodland). Climate warming may benefit it long-term as a warmth-preferring species near the northern edge of its European range. Priority species in some UK Biodiversity Action Plans; target of pond restoration projects in southern England.