Interrupted fern

Sun

Partial shade to full shade; tolerates more sun in cool climates if the soil stays moist.

Water

Keep consistently moist, especially during establishment and hot weather. Avoid prolonged flooding or stagnant soil.

Soil

Humus-rich, moisture-retentive soil with drainage; prefers acidic to neutral conditions but tolerates a range of soils.

Height

2-4 ft (0.6-1.2 m)

Spread

2-3 ft (0.6-0.9 m)

Foliage

Deciduous, upright to arching green fronds with deeply divided leaflets. Some fronds have a central section of dark brown, spore-bearing leaflets that shrivel, leaving a conspicuous interruption.

Growth

Slow to moderate; gradually forms a substantial clump.

Care needed

Low

• Deer resistant
• Cold hardy
• Wildlife

Northern hemisphere months. In Australia, shift them by six.

Difficulty

Easy

Toughness

Fairly tough

Pick your zone, country, light and whether you have pets.

1. Planting day

   1 ft (0.3 m)

2. After 1 year

   1.5 ft (0.45 m)

3. After 2 years

   2 ft (0.61 m)

4. After 3 years

   2.5 ft (0.76 m)

5. After 5 years

   3 ft (0.9 m)

   full size

About 4 years to full size.

From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.

Cats and dogs

Safe

Growth rate

Slow

• Water deeply during dry spells rather than allowing the root zone to dry out.
• Mulch annually with leaf mould or compost, keeping the crown uncovered.
• Plant with the crown at soil level in a sheltered, shaded position.
• Avoid heavy feeding; an annual compost mulch is usually sufficient.
• Leave established clumps undisturbed unless division is needed.

Pruning. Remove dead fronds in late winter or early spring before the new fiddleheads unfurl. Cut close to the base without damaging the crown or emerging growth.

Late winter

Cut away last year's dead fronds before new growth begins.

Early spring

Plant new ferns or divide established clumps if necessary, watering thoroughly afterwards.

Spring

Apply leaf mould or compost around the clump, leaving the crown clear.

Late spring

Check unfurling fronds for slug damage and protect vulnerable new plants.

Summer

Water during dry spells and check for scorching where plants receive direct afternoon sun.

Autumn

Allow fronds to die back naturally; retain fallen leaves around the plant as a loose mulch.

• Plant in groups beneath deciduous trees where soil remains moist, using the upright clumps to give woodland borders structure.
• Combine with hostas and foamflowers for contrasting leaf shapes in shaded beds.
• Use beside a pond or stream above the permanently waterlogged margin.
• Place behind low spring woodland flowers so emerging fronds fill the space as those plants fade.

Garden styles it suits: Woodland, Japanese, Green on green, New England, Pacific Northwest woodland and Low-maintenance.

Plant it with: Hosta, Foamflower, Solomon's seal, Astilbe, Lady fern and North American wild ginger.

Wildlife: Clumps and retained leaf litter provide shelter for small invertebrates. It produces no flowers, nectar or fruit and is usually left alone by deer, though browsing is still possible.

• Brown, crisp frond edges usually indicate dry soil, hot sun or drying wind; water deeply, renew mulch and provide afternoon shade.
• Premature summer dieback can follow drought; restore steady moisture and leave the crown undisturbed, as it may recover the following spring.
• Slugs and snails may damage emerging fronds; hand-pick them and use iron-phosphate bait according to the label if needed.
• Crown or root rot can develop in stagnant, waterlogged soil; improve drainage or move the fern to moist but aerated ground.

Not known to be toxic to people, cats, dogs or horses, although species-specific safety information is limited. No part should be treated as food; do not eat the fiddleheads or other growth.

• Cinnamon fern (Osmundastrum cinnamomeum)

  Its cinnamon-brown fertile fronds are separate, upright structures rather than brown fertile leaflets midway along otherwise green fronds.

• Royal fern (Osmunda regalis)

  It has more open, branching fronds with distinct oval leaflets; its brown fertile portions occur at the frond tips rather than in the middle.

• Ostrich fern (Matteuccia struthiopteris)

  It has strongly tapered, feather-shaped green fronds and separate, narrow fertile fronds that persist through winter; it also spreads more freely by runners.

The common name describes the interrupted outline left by withered fertile leaflets, while claytoniana honours the eighteenth-century botanist John Clayton.

Propagation. Divide a large clump in early spring as growth begins, retaining several buds and a generous portion of roots on each division. Old crowns are tough and slow to replace, so divide sparingly. Propagation from freshly collected spores is possible but slow and requires clean, consistently humid conditions.

Accepted botanical name

Claytosmunda claytoniana

Sources: GBIF (CC BY 4.0). The care and design notes are LandscapeGPT's own.