Osmunda claytoniana
interrupted fern
Eastern North America and eastern Asia
Overview
Osmunda claytoniana is a deciduous fern in the royal fern family, forming a vase-shaped clump of arching fronds 24–48 inches (60–120 cm) tall and 18–36 inches (45–90 cm) wide from a stout, slowly creeping rhizome. The pinnately divided, light green fronds taper at both ends, each with 15–20 pairs of oblong leaflets. On fertile fronds, a few pairs of leaflets near the middle become brown, shrivelled, and spore-bearing, then wither and drop, leaving a visible gap that interrupts the blade and gives the fern its name. These fertile leaflets release green spores in spring before the rest of the frond reaches full size. The clump grows slowly into a dense crown, and old fronds form a fibrous base. It grows in moist to seasonally dry woodland, slopes, and roadside banks, tolerating drier ground than most large ferns. The fronds die back to the crown after frost. Nearly identical fossils date back more than 200 million years to the Triassic.
Native Range
Native to eastern North America, from Newfoundland and Ontario south to Georgia and Arkansas, with a separate population in eastern Asia. It grows in moist deciduous woods, shaded slopes, stream banks, and roadside ditches.Suggested Uses
Used in shade and woodland gardens, along stream and pond banks, and in native fern borders. Suited to moist, shaded slopes and the north side of buildings. Grown as a coarse-textured backdrop among hostas, sedges, and other shade plants.How to Identify
Appearance
Size & Dimensions
Height2' - 4'
Width/Spread1'6" - 3'
Reaches mature size in approximately 4 years
Bloom Information
Ferns do not flower. The fertile leaflets near the middle of the frond release green spores in spring, in April and May, then wither and drop within a few weeks. The sterile portions of the frond continue to expand through early summer.
Detailed Descriptions
Foliage Description
light greenGrowing Conditions
Sun Requirements
Tolerates up to 4 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 part to full shade on moist, humus-rich, acidic soils with a pH of 4.5–6.5, and tolerates drier ground than most royal ferns once established. Consistent moisture produces the tallest fronds, while drought causes early browning. A mulch of leaf litter keeps the shallow rhizome cool and moist. Plants are slow to establish and spread little, forming long-lived clumps. Hardy in USDA zones 3 to 8. It needs no feeding beyond annual leaf mould.Pruning
No routine pruning is needed. Dead fronds are cut away in late autumn or left to shelter the crown over winter. Old fronds are removed in early spring before new growth unfurls.Container Growing
✓ Suitable for container growing
Minimum container size: 3 gallons