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Carex decomposita (Cypress-Knee Sedge)
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© ThePrairiePreacher, some rights reserved (CC-BY-NC) · iNaturalist
Grasses & Sedges

Carex decomposita

Cypress-Knee Sedge

Cyperaceae
Southeastern United States, from Virginia south to Florida and west to Louisiana, in cypress swamps and bottomland forests

At a Glance

TypeSedge
HabitClumping
FoliageSemi-evergreen
Height12-24 inches (30-60 cm)
Width12-18 inches (30-45 cm)
Maturity3 years

Growing Zones

USDA Hardiness Zones

5 - 9
Zone 5Zone 6Zone 7Zone 8Zone 9
These zones indicate the coldest temperatures this plant can typically survive.
What's my zone? →
Frost Tolerancehardy

Key Features

Deer Resistant
Native to North America
Maintenancevery low

Overview

Carex decomposita is cypress-knee sedge, a rare native sedge that in the wild grows epiphytically on cypress knees, rotting logs, and tree bases in deep swamp shade. Plants grow 12-24 inches (30-60 cm) tall and 12-18 inches (30-45 cm) wide. The species name 'decomposita' refers to the compound (decomposed) spikelet structure. Dark green narrow arching leaves form a graceful clump. The epiphytic habit in nature (growing on decaying wood above the swamp waterline) sets the species apart from most common sedges. In cultivation, planted in consistently wet, acidic, humus-rich shade. Dense clustered compound brown spikelets in late spring. The deep-shade, deep-wet tolerance suits this specialist sedge to the most extreme shade-and-wet garden conditions. Semi-evergreen. Hardy to zone 5. Considered rare or threatened in parts of its range. Deer avoid sedge foliage.

Native Range

Carex decomposita is native to the southeastern United States, from Virginia south to Florida and west to Louisiana, in cypress swamps and bottomland forests.

Suggested Uses

Used in wet woodland gardens, swamp edge plantings, and bog gardens. The specialist sedge for the wettest, shadiest conditions. Conservation value, as the species is rare in parts of its range. A botanical curiosity for sedge collectors.

How to Identify

Identified by dark green arching foliage in deep wet shade; in nature, often growing on cypress knees and rotting logs (epiphytic). The compound clustered brown spikelets and the extreme wet-shade habitat confirm the species. A rare specialist.

Appearance

Size & Dimensions

Height1' - 2'
Width/Spread1' - 1'6"

Reaches mature size in approximately 3 years

Colors

Flower Colors

brown

Foliage Colors

green

Fall Foliage Colors

no change

Bloom Information

Bloom Period

~2 weeks
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Spring
Spikelets in May and June. The dark green foliage in deep wet shade is the year-round display.

Detailed Descriptions

Flower Description

Brown to dark brown; in dense clustered compound spikelets

Foliage Description

Dark green; narrow arching

Growing Conditions

Sun Requirements

Partial ShadeFull Shade
Requires 2-5 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

Soil Requirements

pH Range5.0 - 6.5(Acidic)
357912
Soil Types
loam
Drainagewet

Water & Climate

Water Needs

High

Frost Tolerance

hardy

Time to Maturity

2-3 years

Care & Maintenance

Care Guide

Sited in partial to full shade. Wet, acidic, humus-rich soil. Tolerates standing water. Hardy to zone 5. A specialist for extreme shade-and-wet conditions.

Pruning

Cleaned up in early spring.

Pruning Schedule

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early spring

Maintenance Level

very low

⚠️ Toxicity Warning

Non-toxic