Key Facts
- Perennial sedge like marsh plant with distinctive white cottony seed heads
- Native to cool temperate and subarctic wetlands in the Northern Hemisphere
- Grows in acid peaty and waterlogged soils
- Forms tussocks or colonies by short rhizomes
- Flowers and produces cottony seed heads in late spring to summer
- Valued for bog gardens and naturalized wet areas
- Generally cold hardy and tolerant of prolonged saturated soil
- Not known as a common garden toxin but ingestion of fluff has no value
Cotton Grass (Eriophorum angustifolium) is a perennial sedge notable for white, cottony seed heads that add texture to bog gardens and pond edges. It forms tussocks or small colonies in acidic peaty soils that remain wet and is valued for naturalized wet areas rather than dry borders.
Identification
Clumps of erect grassy stems reach about 8 to 24 inches tall with narrow leaves and distinctive white, cottony seed heads produced in late spring to mid summer. Plants form tussocks rather than single crowns and the cottony heads persist long enough to give season‑long interest in wet plantings.
Best uses and where to grow
Use Cotton Grass in bog gardens, along pond margins, or in any naturalized wet area where acidic peat or consistently waterlogged soil is available. It suits open, cool sites and provides texture and winter interest; it is not suitable for well drained or alkaline beds where it will decline.
Planting and spacing
Plant as individual clumps spaced about 12 to 24 inches apart to allow tussocks room to form. Transplant divisions into saturated peat or consistently wet soil so roots establish without drying out; seed can be used but typically requires cold, moist stratification before sowing.
Soil and watering
Thrives only in acidic, peaty soils that remain saturated to waterlogged. Consistent wetness is essential; plants decline if soils dry. Avoid alkaline or freely draining soils and keep planting sites boggy or permanently damp for reliable growth and flowering.
Light and hardiness
Performs best in full sun to part shade with stronger flowering in open, sunny bogs. Hardiness is inferred for USDA zones 2 to 7, making it suitable for cool temperate and subarctic garden locations where soils remain cool and wet.
After flowering and maintenance
Seed heads provide visual interest after flowering and can be left for naturalizing or cut back if a tidier look is preferred. Little routine maintenance is needed beyond keeping the site wet and removing dead or decaying foliage in spring to refresh tussocks.
Spread and naturalizing control
Spreads by short rhizomes to form colonies and tussocks; in consistently wet conditions colonies expand slowly. Reducing water or removing entire tussocks are the primary ways to limit expansion in planted areas where spread is undesirable.
Propagation
Raised from seed or by division of established tussocks. Seed often needs cold, moist stratification to germinate while divisions should be planted into saturated peat or wet soil so they do not dry out during establishment.
Frequently asked questions
- How fast does Cotton Grass grow?
- Individual stems grow each season to about 8 to 24 inches and colonies expand slowly by short rhizomes in consistently wet conditions.
- When does Cotton Grass flower?
- Flowering occurs in late spring to mid summer, with cottony seed heads most visible from about May through July in northern hemisphere climates.
- Is Cotton Grass suitable for a bog garden?
- Yes. It prefers acidic, peaty soils that remain waterlogged and is ideal for bog gardens, pond edges and other wet, naturalized plantings.
- How should I plant divisions?
- Plant divisions into saturated peat or wet soil, keeping roots wet while they establish. Space clumps about 12 to 24 inches apart to allow tussocks to form.
- Will it tolerate dry soil?
- No. Cotton Grass declines if soils dry out and performs poorly in well drained or alkaline conditions, so maintain consistently wet soil for healthy plants.
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