Osmunda

( ox - MUN - duh )

At-A-Glance Information

This genus of ferns includes species which need full sun to light shade and ample water to perform well in the garden. These are large, deciduous ferns that are perfect for woodland edges or when planted in moist, rich soil near bodies of water. Fronds are twice divided, and as they enter dormancy, they turn various shades of orange, brown and yellow. These ferns produce separate fertile and sterile fronds. They are commonly called Royal Fern or Cinnamon Fern, and are ideal for rain gardens, bog gardens, and shaded beds and borders. They can also be massed on slopes for erosion control purposes or used as low-traffic groundcover.

Osmunda Species and Varietals

Osmunda is a member of the plant family Osmundaceae, and includes between 4 and 10 recognized species. The best growing zones for Osmunda vary depending on the species. For more information, see the descriptions below. To find your zone, click here: Zone Map.

Osmunda cinnamomea (Osmundastrum cinnamomeum) (Cinnamon Fern, Fiddleheads, Buckhorn Fern)
Best in USDA hardiness zones 3-10 or Sunset growing zones 1-6, this species reaches 2-6 feet tall and 2 feet wide, and has both sterile and fertile fronds. The species is native to the Americas and Asia, and thrives in moist, acidic wetland environments. In spring, fertile fronds mature to a rich, cinnamon-brown color.

Osmunda japonica (Osmunda nipponica) (Asian Royal Fern, Fiddlehead, Gobi, 고비, Zenmai, ゼンマイ, 薇 , Zǐqí, 紫萁, Juécài, 蕨菜)
This species is native to China, Korea, Taiwan, Japan, and Russia, where it grows in moist woodland areas. These ferns can tolerate open sunlight only if in very wet soils, and can reach up to 3 to 5 feet tall and wide at maturity.

Osmunda regalis (Royal Fern, Flowering Fern)
Does well in USDA hardiness zones 3-10 or Sunset growing zones 1-9 and 14-17, and reaches 6 feet tall and 3 feet wide at maturity. This fern has long frond segments, and can grow in shallow water, thriving in moist environments. Cultivars include 'Cristata' (with crested fronds) and 'Purpurascens' (with purple-red new growth and purple mature stems), and 'Undulata' (with distinct wavy margins on leaflets). This species is considered invasive in New Zealand.

Osmunda spectabilis (American Royal Fern, Royal Fern, Flowering Fern)
This species is native to a region that spans from the eastern half of Canada down through the United States to Argentina. It is a clump-forming deciduous fern. Individual plants can reach up to 2 to 5 feet tall and 2 to 3 feet wide when mature. American Royal Fern grows well in USDA hardiness zones 3 to 10, and thrives in bogs, floodplains, and damp woodlands.

Caring for Osmunda

Osmunda ferns need to be situated in full to partial shade for best results; ideally, they should at most be getting filtered sunlight outdoors. They prefer to be planted in fertile, well-draining but moist soils in areas with high humidity. If local soils are particularly poor in nutrients or do not drain well, make sure to amend the planting area with plenty of organic compost before installing. The ideal soil pH for these ferns is between 4.0 and 6.8. Apply a layer of mulch around the planting area to suppress weed growth, maintain consistent soil temperatures, and to increase soil moisture retention. Water new plantings regularly as they establish a strong root system in their new home. Mature ferns will also need regular waterings, and soil should not be allowed to dry out between irrigations.

Fertilize yearly in early springtime with an application of 2 inches of compost around the base of plants. Pull mulch back before applying, work the compost gently into the soil a bit, water it in, and then replace mulch. These plants are not heavy feeders, and this should be sufficient to provide the necessary nutrients for the active growing and flowering seasons. Prune off any damaged, diseased, or dead growth in springtime to clean up the look of the plant and improve airflow. Divide plants every 3-5 years or when they are overcrowding their allotted space. For instructions on how to successfully divide these ferns, see the Propagation section below. Osmunda ferns are very long-lived perennial plants, able to survive for centuries in the landscape before needing to be replaced. They will also form clumps over time which can be divided, providing new ferns for the landscape indefinitely.

Growing Osmunda in Containers
Osmunda, or Royal Ferns, do well in the ground as well as in containers. Choose a container that has adequate drainage holes on the bottom and is about 2 inches larger than the root ball. Fill the container with well-draining potting mix amended with plenty of organic material, compost, and vermiculite. Apply a layer of mulch around the planting area to suppress weed growth, maintain consistent soil temperatures, and to increase soil moisture retention. Water regularly; Royal Ferns grown in containers will require more frequent irrigation than those grown in the ground. Fertilize yearly in early springtime with an application of 1 inch of compost around the base of the fern. Pull mulch back before applying, work the compost gently into the soil a bit, water it in, and then replace mulch. Prune to remove dead, damaged, or diseased foliage at any time during the growing season. Every few years, these ferns will need to be taken out of their pots and divided. For instructions on how to successfully divide Maidenhair ferns, see the Propagation section below.

Propagation

Osmunda ferns are best propagated via division. This type of propagation is relatively simple; you will need a clean shovel, mulch, fresh soil, compost and/or other organic material, and pots. Division is best done in spring or fall (after the plant has entered dormancy but before it has begun its new spring growth), and needs to be done every few years regardless of whether you have the goal of propagating the plants for best results. To propagate by division, follow these steps:

Gather your materials. Using a shovel, dig up your existing plant. Start from the outside and work your way in to avoid damaging the roots. Once you have worked it up out of the ground, lay it out.
Start to tease apart the roots with your fingers. Once the roots are untangled, separate your plant into segments, ensuring that each one has at least one thick root section.
Prepare your pot(s) or new planting site(s) with amended, well-draining soil. You can either bring in new soil or simply amend your existing soil with compost or other organic material to complete this task. Then, plant your divided ferns in soil at the same height as they were previously, and water thoroughly.
Apply a thick layer of mulch over the new planting to protect it from cold weather as it acclimates to its new home. Then, enjoy watching it sprout.

Problems and Pests

Certain Osmunda species are considered invasive in some regions; see the species descriptions above for more information. Check with local authorities before planting. Osmunda ferns can be susceptible to developing issues with the following pests and diseases in the garden: