Plant problems

Why Are My Lachnagrostis Leaves Curling?

Q: How do I grow lachnagrostis filiformis in the UK?

Lachnagrostis filiformis (blown grass) is a delicate, fine-textured ornamental grass that is best treated in UK gardens as a short-lived annual or biennial, raised from seed and used for its contribution of fine texture and gentle movement in a mixed border or naturalistic planting during the spring and early summer months. From seed: sow in autumn (September to October) in pots or seed trays of gritty, well-drained compost; overwinter in a cold frame or cool greenhouse; the seedlings develop through winter and early spring and produce their ornamental flower panicles from late spring to early summer; alternatively, sow in early spring (March to April) for summer display; surface sow as the very fine seeds need light to germinate; do not cover with compost. Position: an open, sunny to lightly shaded, sheltered position; full sun gives the best and most abundant flower panicle production; a position that catches a light breeze shows the delicate movement of the panicles to advantage. Soil: moderately moist to moist, open, well-drained soil; avoid very dry, drought-prone, or waterlogged soils; a light, open, moderately fertile loam or sandy loam is ideal. The plant self-seeds freely in suitable conditions and may naturalise in a garden with open, disturbed, or lightly cultivated ground; allow seed to shed for self-sown plants the following year. Use: the very fine, cloud-like panicles of blown grass provide a gentle, airy texture in a mixed ornamental border or naturalistic meadow planting; it contrasts beautifully with bolder leaves (hostas, heucheras, alliums) and provides a finer texture than most ornamental grasses; good cut or dried flower.

Q: What is the difference between lachnagrostis and agrostis?

Lachnagrostis and Agrostis are closely related genera of grasses in the family Poaceae; Lachnagrostis was previously included within Agrostis by many authors and has only been recognised as a separate genus by more recent taxonomic treatments. The name Lachnagrostis reflects a key distinguishing feature: the genus name combines 'Lachno' (from the Greek for 'woolly' or 'hairy') and 'agrostis' (grass), referring to the hairy lemmas and glumes that distinguish Lachnagrostis species from the otherwise very similar Agrostis species, in which these structures are typically glabrous (hairless). In practical terms for a UK gardener or naturalist, the two genera are very similar in appearance and in their ecological preferences: both include fine-textured, delicate annual and perennial grasses with very fine, airy panicles; both are found in open, disturbed, or damp habitats; and both can be difficult to distinguish without close examination of the lemma and glume surface under magnification. The main species likely to be encountered in the UK: Agrostis capillaris (common bent), A. canina (velvet bent), A. stolonifera (creeping bent), and A. vinealis (brown bent) are all native UK grasses common in grassland, heathland, and lawns; Lachnagrostis filiformis (blown grass) is an introduced casual plant from the Southern Hemisphere found on disturbed and waste ground, damp soil, and river margins; it is not native to the UK. For garden identification, the very fine, thread-like, nodding, airy panicle of L. filiformis and its introduced-casual status help distinguish it from the native Agrostis species, though magnification is needed for definitive identification.

Q: Which grasses have the finest, most airy flower panicles for a UK garden?

A range of ornamental grasses produce exceptionally fine, airy, light-catching flower panicles that add a cloud-like, gauzy, or transparent texture to a UK garden: Stipa tenuissima (syn. Nassella tenuissima, Mexican feather grass, pony tails): very fine, hair-like, silky, bright green to straw-yellow flowing panicles; one of the finest-textured ornamental grasses; moves beautifully in the wind; semi-evergreen; sun; free-draining soil; widely available. Lachnagrostis filiformis (blown grass): very fine, thread-like, airy panicles that shake and tremble in the lightest breeze; less widely available than stipa; annual or short-lived perennial; moist to moderately moist, open soil. Briza media (quaking grass, doddering dillies): heart-shaped, nodding, locket-like spikelets on hair-thin pedicels that tremble (quake) in the slightest breeze; a native UK grassland grass; sun; calcareous, well-drained soil; one of the most distinctive and charming of all UK native grasses. Briza maxima (greater quaking grass): larger, elongated, pendulous locket-like spikelets; Mediterranean annual; sun; free-draining soil; very easy from seed; excellent cut and dried flower. Agrostis nebulosa (cloud bent grass): a Spanish annual grass with an extremely fine, cloud-like panicle of tiny spikelets; grown as an annual from seed; free-draining, light soil; sun; one of the finest-textured of all annual ornamental grasses. Alopecurus pratensis 'Aureovariegatus' (golden foxtail grass): soft, cylindrical, silky fox-tail flower heads; UK native; moist, fertile soil; sun to partial shade; golden-variegated foliage is as ornamental as the flowers. Deschampsia cespitosa (tufted hair grass): large, open, silvery, cascading panicles of tiny, glittering spikelets in June to July; UK native; tolerates shade and wet soil; one of the best native grasses for damp or shaded gardens.

Lachnagrostis filiformis (blown grass, hair grass) is a delicate, fine-textured, annual or short-lived perennial grass from the Southern Hemisphere, grown ornamentally for its cloud of very fine, airy, thread-like flower panicles that tremble in the lightest breeze. Found in the UK as a casual introduction on damp, open, disturbed ground. Leaves curl and yellow from drought, excessive summer heat triggering premature ripening, or waterlogging on heavy soils.

Drought and insufficient moisture

From moist, open, disturbed habitats in its native Southern Hemisphere range, lachnagrostis does not have the deep roots or drought adaptations of xeric grasses; the fine leaves roll inward and yellow at the tips when the soil dries out excessively. In a container or freely draining soil in a hot, dry UK summer, the fine leaves curl, the airy panicles lose their fresh appearance, and the plant yellows and dries prematurely. Lachnagrostis wilts more rapidly than drought-tolerant grass species in dry conditions.

What to do

Grow in moderately moist to moist, open, well-drained soil; a light, open, moderately fertile loam or sandy loam with consistent moisture through the growing season is ideal. Water in dry spells, particularly when young plants are establishing or during dry spring and early summer weather. In containers, check moisture daily in warm weather and water before the compost dries out completely. A light mulch around the base helps retain soil moisture without causing waterlogging.

Excessive summer heat and premature ripening

Lachnagrostis filiformis is a cool-season annual or short-lived perennial; in a hot UK summer (temperatures consistently above 25 to 27°C) the plant may complete its life cycle earlier than intended, the fine panicles ripen and turn straw-coloured, and the leaves yellow and die back as the plant sets seed. This premature ripening means the main ornamental period is in late spring and early summer in a hot year, not through the whole summer.

What to do

In a hot, dry UK summer, accept that lachnagrostis is primarily a spring to early summer annual grass whose best display peaks before the hottest months. For a later display, sow a second batch of seed in early summer for late summer flowers. Allow the ripened plants to shed seed before removing them; self-sown seedlings may appear in suitable open-ground spots the following spring. The dried, straw-coloured panicles of the spent plant retain some ornamental value as a delicate, dry-texture element in the border through late summer.

Waterlogging on heavy soils

Although lachnagrostis prefers moderately moist conditions, prolonged waterlogging on cold, heavy, poorly draining soils kills the shallow roots, particularly in winter. The plant fails to grow and the leaves yellow and die from the base up on a wet, compacted site. Lachnagrostis is not a bog plant and requires soil that drains freely even if it remains consistently moist at depth.

What to do

Plant in an open-textured, well-drained soil; improve heavy clay with grit and organic matter before planting; avoid low-lying, waterlogged, or compacted areas. Raised beds, slightly elevated planting positions, and south-facing slopes with free drainage prevent the root damage caused by winter waterlogging. As an annual, lachnagrostis can simply be resown in a better-drained position the following spring if the original site proves too wet.

Frequently asked questions

Why are my lachnagrostis leaves curling?

Lachnagrostis leaves curl most commonly because of drought and insufficient moisture (no deep roots or drought adaptations; leaves roll and yellow when soil dries; grow in moderately moist, open, well-drained soil; water in dry spells; mulch to retain moisture), excessive summer heat and premature ripening (cool-season annual; in hot summers the plant completes its lifecycle early and panicles ripen straw-coloured before midsummer; accept this or sow a second batch in early summer; allow seed to shed for self-sown plants), or waterlogging on heavy soils (shallow roots killed by prolonged cold waterlogging in winter; avoid compacted, low-lying, or poorly draining sites; improve clay with grit; annual so easily resown in a better position). Open, moderately moist, well-drained soil in a sunny position is ideal.

How do I grow lachnagrostis filiformis in the UK?

Best treated as a short-lived annual or biennial; raise from seed. Autumn sowing (September to October) in gritty compost; overwinter in a cold frame; flowers from late spring to early summer. Spring sowing (March to April) for summer display. Surface sow: very fine seeds need light to germinate; do not cover with compost. Open, sunny to lightly shaded position that catches a light breeze; full sun gives the best panicle production. Moderately moist to moist, open, well-drained light loam or sandy loam. Self-seeds freely in open, disturbed ground; allow seed to shed for naturalising. Good cut and dried flower; airy, cloud-like texture contrasts with bolder leaves in mixed borders.

What is the difference between lachnagrostis and agrostis?

Closely related genera; Lachnagrostis was previously included within Agrostis by many authors. Lachnagrostis (from Greek for "woolly" + agrostis) is distinguished by hairy lemmas and glumes; Agrostis lemmas and glumes are typically glabrous (hairless). Similar in appearance; definitive identification requires magnification of the lemma surface. UK native Agrostis species: A. capillaris (common bent), A. canina (velvet bent), A. stolonifera (creeping bent), A. vinealis (brown bent). L. filiformis is an introduced casual from the Southern Hemisphere, not native to the UK; found on disturbed and waste ground, damp soil, and river margins.

Which grasses have the finest, most airy flower panicles for a UK garden?

Stipa tenuissima (Mexican feather grass): silky, hair-like, bright green to straw-yellow flowing panicles; sun; free-draining soil; widely available. Lachnagrostis filiformis (blown grass): very fine, thread-like, trembling panicles; moist to moderately moist, open soil; annual. Briza media (quaking grass): heart-shaped, nodding, trembling locket-like spikelets; UK native; calcareous, well-drained soil. Briza maxima (greater quaking grass): larger pendulous lockets; Mediterranean annual; easy from seed. Agrostis nebulosa (cloud bent grass): extremely fine, cloud-like panicle; Spanish annual from seed; light soil. Deschampsia cespitosa (tufted hair grass): large, silvery, cascading panicles; UK native; tolerates shade and wet soil.