Dicksonia squarrosa - Tree Fern

The Dicksonia squarrosa is a tree fern that is much less known than its cousin, Dicksonia antartica. This fern, native to New Zealand, is less imposing than its cousin but also slightly less cold resistant, which makes it suitable for pot cultivation and winter storage in most areas. It is recognised by its ability to form several thin, dark and rough stipes, each topped with a crown of light green fronds carried by a very dark petiole. It takes a suitable climate, soil, and expertise to grow this beautiful, exotic collector's plant successfully.

The Dicksonia squarrosa belongs to the family of Dicksoniaceae. It is an endemic species to the moist forests of New Zealand, with rather slow growth under our latitudes. It consists of underground rhizomes capable of generating several thin stipes (trunks), crossed by a dense network of almost black capillary roots and covered with old brown, dry fronds. These stipes produce 3 to 5 fronds in their upper part, which grow almost horizontally, arranged in an 'umbrella' shape. They are carried by long, hairy petioles of a very dark brown that extend to the tip of each frond. Each frond, soft to the touch, measures about 1.50 m (4 ft 11 in) in length. They are evergreen and each frond has an average lifespan of 2 years when the frost is not too severe, otherwise they "burn" in winter and are replaced by a new crown of fronds the following spring. The entire plant will measure an average of 1.30 m (4 ft 4 in) in height and 1 m (3 ft 4 in) in spread at the age of 10 years. Ultimately, this tree fern does not exceed 3 m (9 ft 10 in) in height and about 1.50 m (4 ft 11 in) to 2 m (6 ft 7 in) in spread. 

Tree ferns are not known for their great hardiness, however, some species including Dicksonia antartica and D. fibrosa are quite hardy without any protection down to -7C°, and even down to -10C° if they are in a sheltered location, without wind. As for the Dicksonia squarrosa, it is commonly accepted that its hardiness does not exceed -5°C for a short period without protection in a sheltered position. Beyond that, winter protection is necessary. It can be reduced to a "straw hat" to protect the future fronds at the top of the stipe (trunk), which is the most sensitive area to cold. In this way, the fern can withstand brief frosts of around -7°C. Another solution is to cultivate it in a large pot and bring it indoors during winter in an unheated or minimally heated conservatory. In addition to its low cold resistance, this tree fern only thrives in the constantly humid atmosphere of woodland and in a humus-rich, moist soil, without any trace of limestone. Its cultivation in the ground is therefore reserved for the mildest areas, in the company of other beautiful acid-loving plants such as large rhododendrons, camellias, mimosas, Eucalyptus, pieris, or Japanese maples.