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Interrupted fern

Osmunda claytoniana · Osmundaceae

Interrupted fern (Osmunda claytoniana)
Photo: Wikimedia Commons (CC BY-SA 2.0 ca)

A large, vase-shaped fern whose tallest fronds are 'interrupted' in the middle by a few brown, spore-bearing leaflets that soon fall, leaving a gap.

Size
3½ ft tall, 3 ft wide
Zones
3 to 8
Light
Part sun to shade
Flowers
Grown for its leaves
Pets
No toxicity recorded
Job in a bed
Specimen

A bed built around interrupted fern

The planner designed this bed around interrupted fern when this page was made: a 12 × 6 ft (3.7 × 1.8 m) English border in zone 6, part shade. It chose the other plants from the 513 that suit those conditions, and says below why interrupted fern stands where it does.

A 12 × 6 ft (3.7 × 1.8 m) bed at eye level in early May: Interrupted fern, Green-and-gold, Astilbe 'Sprite', Formosa toad lily, Japanese anemone 'Honorine Jobert', Hellebore 'Pink Frost', Yellow trout lily, Snowdrop.
A 12 × 6 ft (3.7 × 1.8 m) English border in zone 6, part shade, seen from the path in early May.
1. Interrupted fern15. Japanese anemone 'Honorine Jobert'55. Japanese anemone 'Honorine Jobert'55. Japanese anemone 'Honorine Jobert'52. Green-and-gold22. Green-and-gold22. Green-and-gold23. Astilbe 'Sprite'33. Astilbe 'Sprite'33. Astilbe 'Sprite'33. Astilbe 'Sprite'33. Astilbe 'Sprite'32. Green-and-gold22. Green-and-gold22. Green-and-gold22. Green-and-gold22. Green-and-gold23. Astilbe 'Sprite'33. Astilbe 'Sprite'33. Astilbe 'Sprite'34. Formosa toad lily44. Formosa toad lily44. Formosa toad lily46. Hellebore 'Pink Frost'66. Hellebore 'Pink Frost'66. Hellebore 'Pink Frost'62. Green-and-gold22. Green-and-gold22. Green-and-gold22. Green-and-gold22. Green-and-gold22. Green-and-gold22. Green-and-gold22. Green-and-gold27. Yellow trout lily7. Yellow trout lily7. Yellow trout lily7. Yellow trout lily7. Yellow trout lily7. Yellow trout lily7. Yellow trout lily8. Snowdrop8. Snowdrop8. Snowdrop8. Snowdrop8. Snowdrop8. Snowdrop8. Snowdrop8. Snowdrop8. Snowdrop8. Snowdrop8. Snowdrop8. Snowdrop
From above, to scale. Each circle is one plant, as wide as the room it needs.

The plants

  1. 1 Interrupted fern × 1, green leaves
  2. 2 Green-and-gold × 16, yellow
  3. 3 Astilbe 'Sprite' × 8, pink
  4. 4 Formosa toad lily × 3, purple
  5. 5 Japanese anemone 'Honorine Jobert' × 3, white
  6. 6 Hellebore 'Pink Frost' × 3, pink
  7. 7 Yellow trout lily × 7, yellow
  8. 8 Snowdrop × 12, white

Why this plant

  • The only plant grown for its leaves. Leaf lasts all season, where a flower lasts a few weeks.

Why here

  • Anchors a back corner. At 3½ ft it is among the tallest plants here, and the tallest close the ends of the bed, where they stand in front of nothing.
  • A step in the back row. Next to Formosa toad lily (2½ ft): no two neighbours there are the same height, so the back steps up and down like a skyline.
  • One plant, alone. A feature plant is seen as an object, and needs clear ground around it.

Why now

  • Here for its leaves, spring to frost. They cover the 11 weeks between early March and late November when nothing on the plan is in flower.

Planned as an English border: 5 of the 6 groups (83%) are drifts, longer along the bed than they are deep. The scheme leans cool (pink and purple) and uses yellow for warmth, with white to calm things between them. Interrupted fern is grown for its leaves rather than its flowers.

The planner's own design check: 12 Excellent, 5 Good. It flags one thing to watch: Nothing on this plan is highly poisonous or an aggressive spreader.

Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.

Where interrupted fern goes in a border

At 3½ ft it belongs at the back of a bed. In the planner's ten height classes it is moderately tall (3 to 4 ft).

Its job: specimen. A feature plant with a shape of its own. It stands alone with room around it, and repeats only at a distance.

It has the stature of cinnamon and royal ferns, and unlike them it does not need wet ground. One of the easiest big ferns.

  • A large specimen fern for ordinary garden soil
  • Woodland gardens
  • Structure among hostas

What to plant with interrupted fern

Plants recorded as good partners for it, and what each pairing does:

  • Hosta 'Sum and Substance': bold leaves against its medium ones; happy in the same moist soil.
  • Solomon's seal: adds the flowers, early May to late May; happy in the same moist soil.
  • Astilbe: adds the flowers, late June to mid July; low enough (24 in) to stand in front of it; happy in the same moist soil.

Questions about interrupted fern

Does interrupted fern need sun or shade?

Interrupted fern grows in part sun (4 to 6 hours of sun, including some afternoon sun), part shade (2 to 4 hours of sun, mostly in the morning) and shade (less than 2 hours of direct sun, or bright dappled light). It is one of the few that also put up with deep shade.

It wants soil that stays evenly moist, rich in organic matter, and a good soak in dry spells. It copes with soil that stays wet.

What zones does interrupted fern grow in?

USDA zones 3 to 8. It is hardy to zone 3, which means it survives winter nights down to about −30 °F (−34 °C).

Above zone 8 it struggles: the zones measure winter cold, but a plant's top zone usually means the summers are too hot or the winters too mild for it to rest.

Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.

How far apart should interrupted fern be planted?

2½ ft (75 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 3 ft (90 cm), so a group knits into one patch.

It grows 3½ ft (100 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.

How many interrupted fern plants do I need?

At 2½ ft apart, set out in staggered rows:

  • 2 to fill 10 square feet (about 1 m²)
  • 5 for a single row 10 ft (3 m) long
  • 6 to fill a 4 × 8 ft bed on its own

In a mixed border, plant it as one, with clear ground around it: a feature plant is seen as an object, and a group of them is a thicket.

In the bed above, the planner used one in one group.

Is interrupted fern poisonous to dogs and cats?

No toxicity is recorded for dogs, cats, horses or people, according to NC State Extension.

"Not toxic" is not "edible": a pet that eats a lot of any plant can be sick.

Do deer eat interrupted fern?

Mostly not. NC State lists it as resistant to deer and rabbits. No plant is proof against a hungry deer in a hard winter, but this one is low on the menu.

What does interrupted fern look like in winter?

Interrupted fern dies down to the ground and there is nothing to see until spring. The old stems can be cut in autumn, or left until spring as shelter for overwintering insects.

Is interrupted fern good for bees and butterflies?

Interrupted fern is visited by songbirds.

It is native to the United States and Canada.

More Osmunda

In these guides

Zone guides: Zone 3 · Zone 4 · Zone 5 · Zone 6 · Zone 7 · Zone 8

Every fact on record

Type
Fern
Size
3½ ft (100 cm) tall, 3 ft (90 cm) wide
Plant
2½ ft (75 cm) apart
Height class
Moderately tall (3 to 4 ft)
Place in the bed
Back
Flowers
None: grown for its foliage
Leaves
Medium texture, herbaceous; green
Shape
Vase-shaped, clumping
Hardy in
USDA zones 3 to 8
Light
Part sun, part shade, shade
Soil
Rich, evenly moist
Water
Moderate
Feeding
Light, in spring
Family
Osmundaceae
Comes from
Eastern Canada and the United States
Attracts
Songbirds
Stands up to
Deer, rabbits, wet soil, deep shade

Checked against NC State Extension. Flowering times are for zone 5: later in colder zones, earlier in warmer ones. Toxicity and spread information is a general gardening guide, not veterinary or medical advice, and invasive status varies by region. If a person or pet eats a plant, contact poison control or a vet. Check your local invasive species list before planting anything with a spread warning.