Ornamental · Osmundaceae
Interrupted Fern
Claytosmunda claytoniana
Give it damp shade and rich, acidic soil and this forgiving native fern rewards you with fresh fronds every spring.
Partial shade
Every 3–7 days
USDA 3–8
2–5 ft · 0.6–1.5 m
Overview
If you're new to ferns, the interrupted fern is a wonderfully forgiving place to start, and it settles happily into any shady, damp corner you can offer. Its name comes from a charming quirk in the frond: a few pairs of brown, spore-bearing leaflets sit right in the middle and break up the green, so the leaf looks as though something interrupted it. Those fertile leaflets appear in mid to late spring and quietly fade by summer, leaving a neat green arch you'll be proud of.
This is a genuine native of cool, moist woodlands, and it is built to endure, so you can plant it with real confidence. It takes winters down to -40°F (-40°C) without flinching and simply ignores the deer and rabbits that ruin more delicate plants. Keep the moisture steady and it will slowly grow into a wide, vase-shaped clump that comes back a little bigger and better each year.
Grow it for its lovely texture and its toughness rather than for blooms, since it produces none, and that is nothing to miss. Its closest lookalikes are the cinnamon fern and the royal fern, yet only this one carries that friendly band of brown leaflets across the middle of its fronds, so you'll always know which is yours.
Care
The short version: give it part to full shade, keep the soil evenly moist and a touch acidic, and offer a yearly top-dressing of compost. Once it has settled in, it asks almost nothing of you beyond a drink during dry spells, so you really can't go far wrong.
Light
Part shade suits it best, but don't stress about placement, because this fern is unusually easygoing and takes anything from full shade to full sun. The one thing to watch with sun is water, since it only copes with bright, open spots where the soil stays constantly damp.
Water
Keep the soil consistently moist and never let it dry out, and reach for the watering can more often through dry weather. At heart it's a wetland fern, so you needn't panic about overdoing it, as it happily shrugs off soggy ground and brief spells of standing water that would rot most other plants.
Soil
It loves moist, humus-rich, acidic ground and is happiest around a pH of 4.5 to 6.5. Beyond that it really isn't picky and settles into clay, loam, or sand alike, as long as you keep the moisture coming.
Temperature
Few garden plants are quite this hardy, so you can plant it almost anywhere cold. It copes with a range from -40°F to 86°F (-40°C to 30°C), riding out harsh northern winters and returning faithfully every spring.
Humidity
Like most woodland ferns it enjoys the air on the damp side, ideally around 50% to 80% humidity, but don't let that intimidate you. Steady soil moisture and a shaded, sheltered spot do nearly all of that work for you in the garden.
Feeding
There's very little feeding to remember here, which is one less thing to fret over. A single spring top-dressing of compost or leaf mold is all it wants, gently enriching the soil the way fallen leaves would on a forest floor.
Pruning
You have no routine pruning to keep up with, so you can breathe easy. Simply cut away dead or tattered fronds in late winter or early spring, before the new growth pushes through, to keep the clump looking tidy.
Repotting
It isn't really a pot plant, so think of dividing rather than repotting and let that reassure you. Lift and split established garden clumps every 3 to 5 years, which conveniently perks up a crown that has begun to fade in the middle.
Size & spacing
A grown clump rises 2 to 5 feet (61 to 152 cm) tall and spreads 2 to 4 feet (61 to 122 cm) wide. Give each plant a little room for that full spread so the fronds can arch out gracefully without jostling their neighbors.
When to plant
You plant this fern in spring, once the soil has thawed and begun to warm, and it's happy to wait for you. New fronds unfurl as the season opens, the brown fertile leaflets show up in the middle of each one by mid to late spring, and they fade off by midsummer while the green holds on right through fall.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: spring
- Harvest: Non-flowering; fertile pinnae appear in the middle of the frond in mid-to-late spring and typically wither by midsummer
Hardiness
USDA hardiness zones: 3–8
Temperature: down to -40°C
Troubleshooting
Happily, an interrupted fern gives you very little to fuss over, and nearly every trouble comes back to dry soil or too much sun. Just glance at the fronds and the crown now and then for the early signs below, then treat the real cause and it will bounce back.
Fronds turning brown and crisp along their edges
Try not to worry, because this is almost always simple thirst, and dry soil paired with strong sun is what pushes it along quickly. Your fern likes its roots damp all the time, so give it a good deep soak and tuck a layer of leaf mold or compost around it to hold that dampness in. If it happens to be baking in the noon sun, gently shift it somewhere shadier and it will recover.
Fix:
- Water deeply to keep the soil consistently moist
- Mulch with leaf mold or compost to retain moisture
- Relocate to a shadier site if planted in full sun
A hollow middle with fresh fronds only around the rim
Rest easy, since this is nothing more than the rhizome crown getting older, and it happens to almost every settled clump given time. When spring comes, lift the plant, divide it, then tuck the healthy outer pieces back in and let the tired middle go. Splitting it every few years like this keeps it thriving, and you will get more ferns for free.
Fix:
- Divide the clump in early spring and replant the healthy outer sections
Toxicity
Here's some reassuring news for pet owners: this is a true fern with no known toxins, so you can plant it freely wherever cats, dogs, and other animals wander. It isn't meant for the dinner plate, but a curious nibble won't hurt a soul, and the species is even known for standing up nicely to rabbit and deer browsing.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
You can relax with a cat in the house. Should yours decide to taste a frond, no harm will come of it, though a very large helping of any greenery might leave a sensitive tummy a bit unsettled for a while.
Dogs None
A dog is perfectly safe around this fern. Brushing past or chewing on a frond does no damage at all, and the very worst a big mouthful might bring is a short, harmless spell of an upset stomach.
Horses None
You needn't fret about horses, because this true fern holds nothing that would poison one, and grazing animals tend to walk right past it anyway.
Rabbits None
Rabbits and this fern get along just fine in the same garden. It has a happy knack for bouncing back from a bit of rabbit nibbling instead of doing any harm in return.
Livestock None
Your cattle, goats, and sheep are in no danger near it. Stock usually leave it be, and even a stray mouthful will not trouble them.
Birds None
The fronds hold nothing that could hurt a bird, so your backyard hens and the wild visitors are welcome to poke around it with no worries.
People None
You can handle it with confidence, since there's nothing irritating in it. It isn't something to eat, so give your hands a rinse after digging, more out of good garden habit than any real need.
No documented toxicity. Handle normally and wash hands after working with soil.
Varieties
You won't find a long roster of named selections for this fern, and that's really all fine. The one form worth knowing is simply the wild type itself.
Osmunda claytoniana var. vera
You are looking at the plain wild form of the interrupted fern here, an infraspecific variety that Wherry named and that Kew's Plants of the World Online still recognizes today.
How to propagate
The easiest way to make more interrupted ferns is to split a settled clump rather than wrestle with seed, since this plant carries spores instead of ever setting any.
DivisionModerate
Early spring · 1-2 years
The kindest and surest way to get more of these ferns is to divide a settled clump in early spring. Lift the rhizome crown, split it into pieces, and replant them, remembering the plant creeps along gently by horizontal rhizomes and a fresh division needs 1 to 2 years to find its feet and fill out. It can also sow itself from spores off the fertile leaflets, but that route is slow and finicky, so don't feel you have to try it.
Myths
The interrupted fern grows flowers or seeds.
Take heart, because it never blooms and makes no seed at all. Like every fern it gets around by spores, held here on a band of brown fertile leaflets set into the middle of a frond that is otherwise green and sterile.
Interrupted fern, cinnamon fern, and royal fern are just one plant.
They are really three different species, all sharing the family Osmundaceae. The easy way to spot the interrupted fern is that band of brown fertile leaflets breaking up the middle of each frond, with green leaflets left above and below.