Overview
Carex filiformis (often treated as a synonym of C. lasiocarpa in North American taxonomy) is a rhizomatous perennial sedge in the Cyperaceae family, growing 18–36 inches (45–90 cm) tall and spreading by slender, far-creeping rhizomes to form loose colonies of indefinite width. Stems are slender, triangular, smooth below and slightly rough above. Leaves are narrow, 1–2 mm wide, grey-green, involute (rolled inward), wiry, and often exceed the stems in length. The inflorescence consists of 2–4 terminal spikes: 1–2 slender male spikes 1–2 inches (2.5–5 cm) long at the top, and 1–2 female spikes below, 0.5–1.5 inches (1.5–4 cm) long, cylindrical, with densely packed utricles. Utricles are 3–4 mm long, ovoid, densely pubescent (hairy) — the downy fruit surface is a key diagnostic character. The species is characteristic of fens, bogs, lake margins, and alkaline wetlands, where it often grows in shallow water or on floating mats of peat. In the Pacific Northwest, the closely related C. lasiocarpa is native in similar habitats. Tolerates calcareous and mildly acidic conditions. Does not tolerate drought — requires permanent moisture or standing water.
Native Range
Carex filiformis is native across Europe, from the British Isles and Scandinavia south to central France and east through Russia to Siberia. It occurs in base-rich fens, transition mires, lake margins, and alkaline wetlands. The closely related C. lasiocarpa extends the range into North America.Suggested Uses
Planted in constructed wetlands, fen restoration, bog gardens, and pond margins where permanent moisture is available. Effective for stabilising the margins of ponds and slow-flowing streams. Used in ecological restoration of calcareous fen habitats. Not suited to garden borders or sites that dry out in summer.How to Identify
Appearance
Size & Dimensions
Height1'6" - 3'
Width/Spread1' - 3'
Reaches mature size in approximately 3 years
Bloom Information
Flowering occurs from May through June. Male spikes at the stem apex release pollen by wind over a 2–3 week period. Female spikes develop below, with utricles ripening to light brown by July–August. Seed dispersal is by water and wind.Detailed Descriptions
Flower Description
Brown (male spikes), light brown utricles (female)Foliage Description
Grey-greenGrowing Conditions
Sun Requirements
Requires 4-10 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Care & Maintenance
Care Guide
Plant in full sun to partial shade in permanently wet to waterlogged, base-rich soil with a pH of 5.5–7.5. Space 12–18 inches (30–45 cm) apart. Tolerates standing water to 4 inches (10 cm) deep. In constructed wetlands, plant at the waterline or in shallow water. No fertilisation is needed — the species is adapted to nutrient-poor fen conditions. Monitor spread, as the far-creeping rhizomes can colonise adjacent wet areas.Pruning
Cut back dead foliage in late winter before new growth begins. No other pruning required. Thin colonies by removing sections of rhizome with a spade if spread exceeds the desired area.Pruning Schedule
J
F
M
A
M
J
J
A
S
O
N
D
early spring