Scleranthus biflorus
knawel cushion
Overview
Scleranthus biflorus is an evergreen, mat-forming perennial that builds a dense, bright green cushion resembling a clump of moss or a hard pillow. It reaches only 1-3 inches (2.5-8 cm) tall and spreads 12-24 inches (30-60 cm) wide, spreading over rocks and uneven ground. The tiny, awl-shaped leaves are densely packed on congested stems, giving a smooth, undulating surface. Flowers are minute and green, borne in pairs in summer, and barely visible against the foliage. The cushion stays green year-round in mild climates. It needs sharp drainage and full sun to keep its tight form; in shade or rich soil the cushion loosens and can develop bare patches. Sustained wet, especially in winter, causes the center to rot out. Growth is steady rather than fast, with a young plant taking 2-3 years to form a cushion 12 inches (30 cm) across.
Native Range
Native to Australia and New Zealand, where it grows on rocky and gravelly ground, in alpine and montane areas, and in open well-drained sites.Suggested Uses
Grown in rock gardens, alpine troughs, gravel gardens, and between paving stones, spaced 8-12 inches (20-30 cm) apart. Used as a low green cushion in well-drained sites. Tolerates light foot traffic in paths and crevices.How to Identify
Appearance
Size & Dimensions
Height1" - 3"
Width/Spread1' - 2'
Bloom Information
Flowers are minute, green, and paired, appearing within the foliage in summer and largely hidden from view. They have little visual presence.
Detailed Descriptions
Foliage Description
Bright greenGrowing Conditions
Sun Requirements
Requires 6-12 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
Grows in full sun in gritty, sharply drained soil, including sandy and rocky ground. The tight cushion form depends on sun and lean soil; in shade or fertile soil it loosens and opens up. Watering is needed only in extended drought once established, as constant moisture and winter wet cause the cushion to rot from the center. Top-dressing with grit improves drainage around the crown. Few pests affect it. Bare patches can be top-dressed with grit to encourage rerooting.Pruning
No routine pruning is required. Trim back loose or browning sections to keep the cushion even, and top-dress bare areas with grit so stems re-root. Debris collecting on the surface is removed to prevent rot.Pruning Schedule
J
F
M
A
M
J
J
A
S
O
N
D
summer
Container Growing
✓ Suitable for container growing
Minimum container size: 1 gallons