‘Silver Tree Fern – Ponga’
Native Maori names for this fern include ponga or kaponga, common names include the silver tree fern, or simply the silver fern.
Cyathea dealbata is endemic to New Zealand, growing on the most parts of the North Island and as far South as the Catlins area on the east and to about Karamea on the west of the South Island. The fern is largely absent from Westland, Fiordland and Stewart Island but can be found on the Chatham Islands.
Cyathea dealbata can be found growing in montane forests to lowland forests. Unlike Cyathea medullaris the silver tree fern is not often found growing in isolated positions away from other plant cover. The fern is relatively easy to pick out in dense forest, firstly look up! If the undersides of the fronds are silver and you are in New Zealand its Cyathea dealbata. Secondly the fern also drops its old fronds quickly and retains the stipe bases, this leaves the trunk clean unlike many other New Zealand tree ferns.
The areas in which Cyathea dealbata grow rarely see temperatures drop much below freezing for prolonged periods. This fern in its most southerly habitats on the South Island of New Zealand may be hardy down to -4°C (25°F). This hardiness will have been built up over generations and many juvenile examples found in the UK would not tolerate these temperatures. The fern may take a few degrees of frost before the fronds scald, but would not viable grown outside in most parts of the UK without considerable protection. Therefore in most cases Cyathea dealbata would need the protection of a cold conservatory or heated greenhouse to survive winter in the UK.
Cyathea dealbata is arguably one of the most beautiful tree ferns with its striking silver frond underside, clean trunk and tall upright trunk. The plants golden brown trunk can grow up to 10m tall with a diameter of 45cm (33ft x 18in). The fronds like many Cyathea are less course than the common Dicksonia Antarctica, and are delicate to the touch and easily damaged. The silvery underside of the fronds does not develop until the plant starts to mature at 3-4 years old. When in spore the undersides of the silver fronds punctuated with numerous light brown sori, a truly striking contrast against the normal silver. The fronds grow to around 2-4m long forming a dense canopy of up to 8m (26ft) in diameter. This canopy can consist of over 30 fronds with new fronds standing erect from the centre of the trunk.
In its natural habitat Cyathea dealbata thrives is in filtered sunlight, loose well drained soils with lots of organic matter and plenty of water. However, this species can still withstand some drying out especially mature specimens.
Family Name: Cyatheaceae
Common Names: Silver Tree Fern, Silver Fern
Position: Partial to full shade
Soil: Humus-rich, light, neutral to acid soil.
Growth Rate: medium – slow
Eventual spread: 8m.
Max Height: 10m (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.