Gymnocarpium dryopteris aka Common Oak Fern

Gymnocarpium dryopteris is a small fern called northern oak fern. Other names include western oak fern and common oak fern. It is native across temperate parts of the Northern Hemisphere. Its range covers parts of Europe, Asia, and North America. It is native to Britain and Ireland as well. Wild plants grow in damp, shady woods and along streams. They also grow on wet cliffs and favour mixed conifer woods. The species occurs in both wetlands and other sites.

This deciduous fern forms low mats and can build broad colonies. Its underground rhizomes help it spread across the ground. The bright green fronds have a clear triangular shape. Each frond divides two or three times into smaller parts. Fronds measure about 0.3–0.7 feet (0.1–0.2 metres) long and wide. The RHS describes plants reaching about 1 foot (0.3 metres) tall. Its wider garden range reaches 1.6 feet (0.5 metres). Mature clumps can spread 1.6–3.3 feet (0.5–1 metre). Plants may take five to ten years to reach full size.

Grow oak fern in deep shade with shelter from exposure. The RHS lists north-, east-, and west-facing sites as suitable. It needs moist soil that lets excess water drain away. Loam and sandy soils both suit it. Choose acid to neutral soil with plenty of leaf matter. Garden compost can help enrich the planting site. The RHS gives it a UK hardiness rating of H5. Chicago Botanic Garden lists USDA zones 5–7 for this species.

Oak fern works as ground cover in a woodland garden. Its green fronds bring light colour to dark planting areas. Use it in beds, borders, and informal cottage gardens. Mass planting shows its leaf shape and low, spreading form. PFAF also lists containers and cut foliage among its uses. The plant loses its fronds rather than keeping year-round cover. Cut back the fronds in autumn as they fade. Divide plants in spring, or sow ripe spores at 59°F (15°C).

The RHS reports few usual pest or disease problems. PFAF does not flag the species as a weed. It lists no known edible uses or medicinal uses. It also reports no known hazards, but gives no detailed safety findings. Reports of elk and grizzly bears eating it do not establish human edibility.