Marsh fern
Thelypteris palustris · Aspleniaceae
Delicate, pale green, upright fronds rise singly from creeping rhizomes in wet meadows and marshes, in sun or shade.
- Size
- 24 in tall, 3 ft wide
- Zones
- 3 to 8
- Light
- Full sun to part shade
- Flowers
- Grown for its leaves
- Pets
- No toxicity recorded
- Job in a bed
- Carpet
A bed built around marsh fern
The planner designed this bed around marsh fern when this page was made: a 12 × 6 ft (3.7 × 1.8 m) English border in zone 6, part sun. It chose the other plants from the 367 that suit those conditions and its wet soil, and says below why marsh fern stands where it does.
The plants
- 1 Marsh fern × 1, green leaves
- 2 Mouse-ear coreopsis 'Nana' × 16, yellow
- 3 Lingonberry × 8, pink
- 4 Northern sea oats × 5, tan
- 5 Joe Pye weed 'Little Joe' × 3, pink
- 6 Mountain hydrangea 'Tuff Stuff' × 1, blue
- 7 Quamash × 12, blue
Why this plant
- The only plant grown for its leaves. Leaf lasts all season, where a flower lasts a few weeks.
Why here
- In the middle. At 24 in it is the step between lingonberry (8 in) in front and Joe Pye weed 'Little Joe' (4 ft) behind: each is seen over the one before.
- One plant. Three or more is usual for a plant of this kind, and reads better.
- Fine leaf against bold. Joe Pye weed 'Little Joe' is beside it: the strongest contrast of leaf there is.
Why now
- Here for its leaves, spring to frost. They cover the 21 weeks between early March and late November when nothing on the plan is in flower.
Planned as an English border: 4 of the 5 groups (80%) are drifts, longer along the bed than they are deep. Joe Pye weed 'Little Joe' and northern sea oats anchor the back corners of the bed: the tallest plants on the plan stand there. The flowering is at its height from late May, with 3 kinds out together.
The planner's own design check: 13 Excellent, 3 Good, 1 Satisfactory. It flags one thing to watch: Marsh fern spreads aggressively. Northern sea oats spreads aggressively.
Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.
Where marsh fern goes in a border
At 24 in it belongs in the middle of a bed. In the planner's ten height classes it is medium short (18 to 24 in).
Its job: carpet. A groundcover planted in threes and fives to cover the soil: along the front, and just behind it.
One of few ferns for full sun, provided its feet are wet. It runs freely and knits a wet bank together, so it is not for a small pond.
- Wet meadows and marsh edges
- Holding wet banks
- A fern for sun
What to plant with marsh fern
Plants recorded as good partners for it, and what each pairing does:
- Blue flag iris: adds the flowers, late May to late June; happy in the same wet soil.
- Swamp milkweed: adds the flowers, early July to early August; tall enough (4 ft) to stand behind it.
- Joe Pye weed 'Gateway': adds the flowers, late July to mid September; bold leaves against its fine ones; tall enough (6 ft) to stand behind it.
Questions about marsh fern
Does marsh fern need sun or shade?
Marsh fern grows in full sun (6 or more hours of direct sun a day), part sun (4 to 6 hours of sun, including some afternoon sun) and part shade (2 to 4 hours of sun, mostly in the morning).
It wants moist to wet soil, of average fertility, and plenty of water.
What zones does marsh 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 marsh fern be planted?
24 in (60 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 24 in (60 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many marsh fern plants do I need?
At 24 in apart, set out in staggered rows:
- 3 to fill 10 square feet (about 1 m²)
- 6 for a single row 10 ft (3 m) long
- 10 to fill a 4 × 8 ft bed on its own
In a mixed border, plant it as threes and fives, along the front and just behind it.
In the bed above, the planner used one in one group.
Is marsh 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 marsh fern?
Mostly not. NC State lists it as resistant to deer. No plant is proof against a hungry deer in a hard winter, but this one is low on the menu.
Will marsh fern spread?
It spreads sideways, by runners or roots; the risk of it taking over is high. Spreads quickly by creeping rhizomes in wet soil. Plant it where it has room.
What does marsh fern look like in winter?
Marsh 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 marsh fern good for bees and butterflies?
Marsh fern is visited by moths.
It is a host plant: the caterpillars of marsh fern moth feed on its leaves. A butterfly can only lay its eggs on its host plants, so these do more for it than any nectar flower.
It is native to the United States.
More Thelypteris
- New York fern Thelypteris noveboracensis
- Southern shield fern Thelypteris kunthii
In these guides
- Plants for wet soil and rain gardens
- Deer-resistant plants for shade
- Pet-safe plants for a sunny border
- Pet-safe plants for shade
- Native plants for shade
- Plants for butterflies
- Groundcover plants
Zone guides: Zone 3 · Zone 4 · Zone 5 · Zone 6 · Zone 7 · Zone 8
Every fact on record
- Type
- Fern
- Size
- 24 in (60 cm) tall, 3 ft (90 cm) wide
- Plant
- 24 in (60 cm) apart
- Height class
- Medium short (18 to 24 in)
- Place in the bed
- Middle
- Flowers
- None: grown for its foliage
- Leaves
- Fine texture, herbaceous; green
- Shape
- Upright, spreading
- Hardy in
- USDA zones 3 to 8
- Light
- Full sun, part sun, part shade
- Soil
- Average, moist to wet
- Water
- High
- Feeding
- None needed
- Family
- Aspleniaceae
- Comes from
- North America, China, and Japan
- Attracts
- Moths
- Host plant for
- Marsh fern moth
- Stands up to
- Deer, heat
Checked against NC State Extension and VASCAN (plants of Canada). 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.