Growing interrupted fern plants, Osmunda claytoniana, is easy. Native to the Midwest and Northeast, these shade-tolerant plants grow in woodland sites. Gardeners add them to plantings of Solomon’s seal and hostas, or use the ferns to create a shaded border. Interrupted ferns even do well as erosion control plants on shaded slopes.
What is an Interrupted Fern?
Interrupted fern plants grow a vase-shaped rosette of erect to nearly erect 2 to 4 foot (61 cm. to 1 m.) high leaves. The common name for these ferns is derived from the broad fronds being “interrupted” in the middle by three to seven spore-bearing leaflets, called pinnae.
These middle leaflets, which are also the longest ones on the frond, wither and fall off in midsummer leaving a blank space or gap on the stem. The leaflets above and below this interruption are sterile – they do not bear sporangia.
Interrupted Fern Care
This eastern North America native plant grows well in USDA zones 3 to 8. In the wild, it grows in shaded sites that are moderately wet. Growing interrupted ferns prefer sites with filtered sunlight, moist conditions, and sandy loam soils that are slightly acidic.
Interrupted fern care is minimal as long as the soil has adequate organic content, there is sufficient humidity, and the site offers protection from prevailing winds to prevent drying out. The plants may grow in more direct sunlight if their roots are in moist soil.
In spring, the plant’s dense mass of roots or rhizomes may be divided. These rhizomes are commercially harvested to create orchid peat used as a rooting medium for epiphytic orchids.
Interrupted Fern vs. Cinnamon Fern
Distinguishing interrupted fern from cinnamon fern (Osmunda cinnamomea) is difficult when just infertile leaves are present. Here is some interrupted fern info to help tell these plants apart:
- Cinnamon fern petioles are more woolly-brown.
- Cinnamon fern leaflets have pointed tips versus rounded tips of interrupted ferns.
- Cinnamon fern leaflets also bear tufts of persistent, woolly hairs at the base of their stems.
- Cinnamon ferns bear sporangia over the entire leaflet, whereas interrupted ferns plants only in the middle of their fertile leaves.
For more interrupted fern info, contact a local nursery or extension office in your area.