Cyathea dealbata - Silver Tree Fern

Although less well-known than Cyathea cooperii, Cyathea dealbata is perhaps the most beautiful tree fern in New Zealand. This species is adorned with large fronds with silver undersides, hence its common name silver fern. The elegant plant has a dark false trunk (stipe) and carries an opulent crown of large fronds. This fern is so iconic that an image of its fronds has been chosen to adorn the official jersey of New Zealand's national rugby union team, the famous All Blacks. Being an exotic centrepiece in itself, it will suit a partially shaded terrace throughout the summer and will be a highlight in a shaded conservatory in winter. Cultivating this wonderful plant requires a certain expertise.

Cyathea dealbata belongs to the large Cyatheaceae family, whose members inhabit the humid tropical and subtropical regions of the Southern Hemisphere. It is a species of warm and humid temperate climate that can only withstand weak and brief frosts in sheltered situations. The fronds will burn at -4°C (24.8°F), and the trunk will not survive below -8°C (17.6°F). In nature, this fern needs a constant climate all year round, characterised by regular and significant rainfall and a temperature that varies seasonally by only 10 to 18°C (50 to 64.4°F), 15 to 20°C (59 to 68°F) or 18 to 25°C (64.4 to 77°F). It grows in partial shade, in cool, light, leached acid soils, that are poor in organic matter but rich enough in minerals.

The plant initially shows a rather slow growth, even in a warm temperate greenhouse. It develops a thick stipe (20 to 40cm (8 to 16in) in diameter) that can reach 4 to 5m (13 to 16ft) in height. This false trunk is made up of interlaced rhizomes covered with dry adventitious roots and the brown, scaly, papery remnants of the petioles of the old leaves. The base of the fronds is also covered with brown scales, giving them a coarse fur-like appearance. The petiole, on the other hand, is silver in colour. The young, rolled-up fronds, called croziers, are also scaly, and they unfold into large, finely divided, light green fronds measuring 2 to 3m (7 to 10ft) in length. The underside of the mature fronds (over 1 year old) is silver in colour. They are produced in the upper part of the stipe, one after the other, without interruption if the plant is kept above 10°C (50°F). Each one is traversed by a silver-coloured rachis. The fronds are evergreen and each has an average lifespan of 2 years when frosts are not too severe.

Tree ferns are not known for their great hardiness, and Cyathea dealbata is no exception. The best solution is to cultivate it in a large pot to be brought indoors in winter in a conservatory kept frost-free or very lightly heated. In addition to its low cold resistance, this tree fern only thrives in the shaded and humid atmosphere of an understory and in light, cool soil without any trace of limestone. Therefore, its cultivation in open ground is reserved for the mildest regions. It seems that mature plants appreciate the sun, which is very rare among ferns.

The Maoris used the fronds of the Silver Fern to find their way in the forest during moonlit nights. Like Hansel and Gretel, they placed its reversed leaves at regular intervals, as their silver scales reflect the light.