How to Plant & Grow Cinnamon Fern (Osmundastrum cinnamomeum)

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how to plant cinnamon fern how to grow cinnamon fern
Cinnamon fern is a North American native that grows well in damp or saturated soils. bobistraveling / CC BY

Cinnamon fern, so named for the slender, rusty brown appearance of its central spore-bearing fronds, belongs to Osmundaceae, the royal fern family. Osmundaceae contains approximately six extant genera numbering a total of 20 to 25 species (some botanists contest the classification of certain species). An old family, ancestors of current royal fern species could be found over 250 million years ago during the Permian Period – making extant ferns truly living fossils in both function and appearance.

Cinnamon fern in particular has been around for at least 75 million years based on fossils discovered in ancient rock beds. Still often classified as Osmunda cinnamomea, recent DNA findings reclassified cinnamon fern as Osmundastrum cinnamomeum – Osmunda cinnamomea is no longer an accepted name amongst taxonomic databases.

Facts, Benefits & Uses of Cinnamon Fern

benefits of cinnamon fern in ponds
Wildlife, such as the veery, depend on cinnamon fern for food and cover for their young. Cephas / CC BY-SA

Native to eastern North America ranging from as far southwest as Texas and as far northeast as Newfoundland, cinnamon fern can be readily found in damp woods, wetlands like bogs, fens, and swamps, along riverbanks, and in seasonally flooded areas whether in the mountains or lowlands. If an area has damp, acidic soils and at least partial shade, cinnamon ferns are likely to be found.

They make unique additions to gardens, as they provide a prehistoric feel while incorporating myriad ecosystem benefits. Ferns in general are well known for their ability to filter toxins out of soil and groundwater.

More specifically, cinnamon ferns directly benefit a multitude of animal and insect species. The tender young fiddleheads are an important food source for ruffed grouse in the spring, while hummingbirds and yellow warblers utilize the plant’s protective downy “fur” as a soft nest lining for their young. The large, draping fronds of the mature ferns provide cover from predators for whitetail deer fawns and the nests of veeries and brown thrashers, and many native insect species lay their eggs on the undersides of the leaves.

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Cinnamon Fern Fact Sheet:
Herbaceous Perennial
USDA 3 – 10
Partial sun to full shade
N/A; Sporangia active May-June
Height 61 – 182 cm (24 – 72 inches); Spread up to 152 cm (60 in)
2.5 – 5 cm (1 – 2 in) above roots
pH 4.5 – 7.5

Cinnamon Fern Growth, Hardiness & Climate

cinnamon fern growth and hardiness
The central fertile fronds of cinnamon fern are what give the plant its name, and appear from May-June.

A low maintenance slow grower, there is little concern about cinnamon fern overtaking a pond garden or wetland. They can grow to a maximum adult height that ranges from 2 to 6 feet, although closer to 3 feet is considered average. Large, vibrant fronds enable the plant to reach a circumference of up to 5 feet, so it’s recommended that each fern be placed at least 6 feet apart. Their maximum size typically takes several years to achieve.

Native to the eastern US and eastern Canada, cinnamon fern prefers damp, shady, cool locations. In nature, it’s typically found in damp woods, bogs, and along shaded streambanks. Excessive heat, sun, and, most especially, dryness can cause stunted growth, sunburned leaves, or plant death. USDA hardiness zones 3 through 10 suit O. cinnamomeum best, so long as it has ample access to water.

As a fern, this plant lacks flower structures and instead reproduces via spores. Its large, striking green fronds are infertile, but typically from May through June it produces fertile fronds that erupt from the center of the plant, covered in tiny bead-like structures known as sporangia. These fertile fronds are narrow and tall, while the sporangia covering them are a rusty-red color. This gives rise to the fern’s name, as these central fronds resemble cinnamon sticks. Each sporangia contains thousands of spores, which are spread via wind and animals moving through the underbrush. By mid-summer, only the infertile green fronds remain on the plant.

How to Plant Cinnamon Fern In Ponds

how to plant cinnamon fern
Cinnamon fern fiddleheads will begin to emerge shortly after the last spring frost. Danny Schissler / CC BY-SA

As might be expected from an organism that’s been around for over 70 million years, cinnamon fern is quite hardy and adaptable. Give them moisture, shade, and at least semi-acidic soil, and you’ll have a prehistoric plant friend for many years. Planting is more successful when done in the spring when there’s no danger of frost. If planting multiple cinnamon ferns, plant each at least 6 feet apart to allow for growth.

If your soil is alkaline, lay down a one to two inch layer of compost that contains acidic ingredients like pine bark, pine needles, coffee grounds, and etcetera, then mix it into the soil to about a foot deep. Then simply dig a hole that’s just large enough to accommodate the fern’s roots, plant, and water enough to saturate the soil.

Unless you want to be watering daily, it’s best to plant cinnamon fern in soils that are naturally damp but well-draining, so placing it marginally along the edge of your pond will work well. Some gardeners have success growing them in one to two inches of water. Planting baskets aren’t necessary, but can be used, though this will largely block the fern’s ability to naturally spread via rhizomes. Spreading is slow and unaggressive, and easy to mitigate if desired.

How to Care For Cinnamon Fern

how to care for cinnamon fern
Photo by James St. John / CC BY-SA 2.0

As stated above, provide cinnamon fern with at least partial shade and damp, acidic to neutral soil and it will be happy. Not much care is needed, though it prefers its feet wet so if there’s a dry spell or you live in a hot area you will likely need to water cinnamon fern to keep the soil damp. If you stick your finger in the soil and it’s damp an inch or two down, no watering is required. Protect it from excessive wind, as this can damage the delicate fronds. They can tolerate up to 6 hours of sunlight, but will need to be consistently kept moist.

If your soil isn’t naturally acidic, each spring you can place a thin layer (ideally half an inch or less for established plants, or 1-2 inches if the fern has only just been planted) of mulch that includes acidic materials like pine needles, pine bark, oak leaves, or a bit of coffee grounds in a wide radius around the base of the plant. This will provide not only acid content, but also nutrients to promote spring growth. You can also clip any dead or dying fronds and add them to the mulch.

As desired, in the spring you can separate plants into new individuals by gently digging up and cutting the root ball cleanly with a knife or scissors, then replanting and watering generously. Skip watering if you’re planting them in a boggy, wet area. As always, clean any dropped foliage from your pond to maintain healthy water quality.

How to Winter Cinnamon Fern

In southern regions, cinnamon fern is an evergreen plant so long as frost doesn’t occur and it has regular access to water. In more northern climes, like the American Midwest or Canada, cinnamon fern is a deciduous plant and will naturally die down once the first frost hits.

You won’t need to do anything to prepare the plant for this – as summer winds down, it’ll start the process of devoting energy to root storage rather than growth. Its starchy roots will sustain the plant beneath the soil through winter, and then nifty light and temperature sensing molecules in the plant will trigger spring growth once the soil reaches a particular temperature.

Is Cinnamon Fern Toxic, Poisonous or Invasive?

As with any plant, cinnamon fern should only be grown inside of its native range. Outside of the US and Canada, it is technically invasive, though it’s not known to overtake areas. For a list of ferns native to the UK, check out this guide. For a list of ferns native to the US organized by region, click here.

Cinnamon fern is not known to be toxic to humans or animals, including fish. However, some other fern species do contain toxic carcinogens, so do be careful when purchasing. Just because someone sells plants does not necessarily mean that they know a great deal about them; plants are often mislabelled, particularly when not obtained directly from a recognized native plant nursery.

To tell for certain if you have a cinnamon fern, check the undersides of its leaves – cinnamon ferns have woolly, cinnamon-colored clusters of hair at the base of each pinnae (pinna), near the stalk at the center of each leaf. If you see small brown dots, these are not the furry tufts that we’re talking about – these are called sori, which contain spores, and do not exist on cinnamon fern leaves. Remember, cinnamon fern spores are found only on the central, brown fronds.

Is Cinnamon Fern Edible? Will Fish Eat it?

Cinnamon fern is edible, with wildlife and, historically, Native Americans eating the tender fiddleheads in the spring. Your fish are not likely to eat it as it’ll be planted in soil, but if you do plant it in very shallow water where smaller fish might be able to swim up to it, they may nibble the roots. This should not harm them or the plant.

Where to Buy Cinnamon Fern & Seeds? (UK & US)

Cinnamon fern is easily obtained in North America from a variety of plant nurseries as well as online outlets. Elsewhere in the world, you’ll likely have to order it online (but, remember, always seek out plants that are native to your region!).

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