Blechnum filiforme
Climbing Hard Fern, also known as Thread Fern, is a remarkable endemic New Zealand fern with a fascinating two-stage life cycle, beginning as a small creeping juvenile with elliptic-oblong toothed leaflets measuring 50-250mm long, then transforming into a high-climbing adult that scales forest trees with strongly dimorphic fronds reaching up to 700mm long. The mature plant produces distinctive narrowly ovate-elliptic sterile fronds with pointed triangular leaflets, while the fertile fronds display the plant's most characteristic feature - extraordinarily long and thread-like leaflets that give this species both its common and scientific names (filiforme meaning "thread-shaped"). Found from the North Island to the north coast of the South Island in coastal and lowland forests, this unique climbing fern creates spectacular vertical displays as it ascends through the forest canopy, making it an exceptional choice for woodland gardens with established trees where its climbing habit can be fully appreciated and its distinctive thread-like fertile fronds create dramatic architectural interest. native ferns
Image credit: Climbing Hard Fern (Blechnum filiforme). Wikipedia
| Scientific Name | Blechnum filiforme (syn. Icarus filiformis) |
|---|---|
| Height | High-climbing (several meters when mature) |
| Spread | Climbing and spreading via rhizomes |
| Water Needs | High (forest native) |
| Light | Partial shade to shade |
| Frost Tolerance | Good (lowland to coastal) |
| Salt Tolerance | Low to moderate (coastal forests) |
| Growth Rate | Moderate (slow juvenile, faster climbing) |
| Lifespan | Long-lived perennial |
Climbing Hard Fern thrives in New Zealand's temperate coastal and lowland climates, particularly in areas with consistent humidity and protection from extreme conditions. It performs best in northern and western coastal regions.
| City | Climate Suitability |
|---|---|
| Whangārei | Ideal |
| Auckland | Ideal |
| Hamilton | Good |
| Tauranga | Ideal |
| Rotorua | Good |
| Gisborne | Ideal |
| New Plymouth | Ideal |
| Napier | Good |
| Whanganui | Good |
| Palmerston North | Good |
| Wellington | Ideal |
| Nelson | Ideal |
| Christchurch | Moderate |
| Dunedin | Moderate |
| Invercargill | Poor |
Climbing Hard Fern has specific soil and support needs:
Forest understory preferences:
High moisture needs:
Best used in shaded courtyards, ferneries, and mounted displays where its thread‑like fertile fronds can be appreciated against dark bark.
Climbing Hard Fern requires minimal pruning:
The unique climbing habit and dramatic thread-like fertile fronds are the main attractions and should be preserved through minimal intervention.
The best time to plant Climbing Hard Fern is during spring when active growth begins and establishment is most successful.
Choose a site with:
Water regularly to maintain consistent soil moisture and provide protection from direct sunlight. This unique climbing fern requires patience as it establishes its juvenile stage before beginning its climbing phase.
Growing from spores is the primary propagation method:
Division is possible but requires care:
This climbing fern requires specialized care and is best suited for experienced fern growers or botanical collections with appropriate forest conditions.
Climbing Hard Fern (Blechnum filiforme) represents one of New Zealand's most specialized fern adaptations and botanical curiosities:
Today, Climbing Hard Fern serves as a remarkable example of evolutionary adaptation in New Zealand's flora, representing the unique solutions plants have developed to thrive in specific environmental niches, making it a prized specimen for botanical collections and specialist fern gardens.
Provide appropriate forest conditions including shade, consistent moisture, high humidity, and suitable climbing support. This specialized fern requires understanding of its unique growth cycle and habitat preferences.
Climbing Hard Fern is the perfect plant for creating dramatic vertical interest in forest gardens - the thread-like fertile fronds are absolutely unique in New Zealand's flora and create stunning architectural effects as they climb up tree trunks or support structures. Be patient during the juvenile creeping stage - this is completely normal and necessary before the spectacular climbing phase begins. Position it against dark tree bark where the delicate thread-like fronds will show to best advantage. This is definitely a plant for fern enthusiasts who appreciate botanical rarities. The key is providing forest conditions: shade, humidity, rich organic soil, and a good climbing support like a tree fern trunk or rough-barked tree.
Learn more about New Zealand's unique ferns in Native Ferns.
Blechnum filiforme (often treated as Icarus filiformis) is a dimorphic climbing fern. Juvenile plants creep with elliptic, toothed leaflets; adults climb high with narrowly ovate sterile fronds and remarkable thread‑like fertile fronds that hang in clusters, giving a delicate, filigreed appearance.
Endemic to New Zealand’s coastal and lowland forests of the North Island and northern South Island. Grows in humid, sheltered sites on tree trunks and rough bark, and occasionally on rocks and banks with ample organic material.
Climbing habit helps access light in shaded forests. Thread‑like fertile fronds produce spores dispersed by wind; creeping juveniles knit mossy substrates, adding structure for invertebrates and epiphytes.
Contributes vertical texture and biodiversity in coastal forest canopies. In cultivation, it brings authentic forest character and supports microhabitats on mounted substrates.
Use coarse mixes (orchid bark, fern fibre, pumice). Provide vertical support to encourage the adult phase. Keep consistently moist, increase humidity in summer, and feed lightly with a fern‑safe fertiliser in spring.
Trim damaged fronds; avoid heavy feeding and low humidity. Manage slugs/snails on tender new growth. Ensure airflow to prevent fungal issues without drying the plant.
Best in shaded courtyards, ferneries, or mounted displays where thread‑like fertile fronds can be appreciated against dark bark. Combines well with nikau, filmy ferns, and shade epiphytes.
Not threatened. Protect coastal forest habitats and mature host trees; avoid removing epiphytic substrates. Use eco‑sourced stock in restoration and education collections.
Blechnum and allied ferns appear across rongoā Māori and practical uses, including lining of earth ovens and application of frond material as poultices. Their presence signals healthy wai and sheltered ngahere (forest) conditions.
Today, thread fern is appreciated for its fine frond texture in shaded gardens and is used to restore damp, sheltered understories where it helps retain soil moisture and suppress weeds.
