‘Black Tree Fern – mamaku’
The native Maori names for this imposing king of the New Zealand tree ferns include mamaku, katata, korau, or pitau. Cyathea medullaris is commonly known as the black tree fern and king fern.
Cyathea medullaris grows on the North and South Islands, Stewart Island, Three Kings Island and the Chatham Islands of New Zealand. The species also grows on several pacific islands including Pitcairn, Marquesas, Samoa, Tahiti and most notably Fiji. The fern can be found growing from sea level to 600m (2000ft), in lowland forest throughout the North Island. In the South Island its distribution is more localised. It is fairly common in wetter coastal areas down the west coast and can be found as far south as the fiordlands. It is less common on the east coast occurring down to Kaikoura, with isolated examples found on the banks peninsula and eastern Otago.
The occurrence of the species around Northland, Auckland, and Waikato characterise the landscape. It is not uncommon too see a grove of the scruffy looking mamaku growing isolated in a field or in the Coromandel Peninsula hillsides completely and gullies completely covered.
This fern only grows in the more temperate regions above and would rarely if ever be exposed to temperatures as low as 0°C (32°F). Therefore this is not going to be viable in the UK without very favourable micro climates and a lot of tender loving care. If you have a cool conservatory that you can overwinter a specimen in and then move into a sunny position in the summer this would be ideal. Wherever you choose to grow the ‘king of ferns’ you must keep it well watered and planted in a humus rich free draining matter.
Cyathea medullaris is a striking fern. The trunk is slender, black and covered with hexagonal stipe bases. The elegant fronds grow up to 6 m (20ft) long and 2m (7ft) wide, and arch upwards from the crown. The mamaku can grow up to 20m (66ft) tall, and about 60cm (24”) in diameter at the base. The upper surfaces of the fronds are dark green and shiny and the undersides a paler jade green. When new fronds emerge they look like they have the skin of a brown bear, covered in thick dark hair. Towards the crown of the trunk these hairs are visible between the stipe bases, but less so were fronds have fallen.
The condition in which Cyathea medullaris will thrive is with good light with shelter from cold winds. The mamaku will also need a well drained soil with lots of organic matter, high in nitrogen and plenty of water. This species will not tolerate frosts so be prepared to move it undercover from its summer position.
Family Name: Cyatheaceae
Common Names: Black Tree Fern, King Fern
Position: Sunny position, sheltered from cold winds
Soil: Humus-rich, well drained, neutral soil.
Growth Rate: medium
Eventual spread: 12m.
Max Height: 20m (less cultivated).
Hardiness: Not Hardy – will tolerate conditions down to 0°C the foliage is easily lost in frosts.
Winter tips: Keep in cool conservatory or heated greenhouse.
Summer tips: Keep moist, water daily during the hotter periods.