‘Slender Tree Fern’
The name Dicksonia squarrosa derives from:
Dicksonia – named in honour of James Dickson, 1738-1822, a British nurseryman.
squarrosa – means ‘having scales or scale-like overlapping leaves or bracts’.
The Maori names for this tree fern include ‘Wheki’ and ‘tirawa’ other common names include ‘Slender Tree Fern’ due its relatively slim trunk, ‘brown tree fern’ and ‘hard tree fern’.
D. squarrosa is endemic to New Zealand’s North and South Islands, Three Kings Island, Stewart Island and Chatham Islands. It is found growing abundantly in coastal – montane forest and is widely regarded as the most common New Zealand tree fern growing in the wild. The fern is particularly common on the western coast of the South Island, found growing on poor or swampy soils. The ferns grows from sea level up to elevations of 760m, therefore the plant should be hardy to around -4°C (25°F). Therefore this fern is not fully hardy in the UK.
D. squarrosa is an attractive, fast-growing tree fern which develops a slender black trunk growing up to 7m x 20cm (23ft x 8 inches) and fronds that range in length from 1.2m-2.4m (4-8ft). However, plants can grow substantially larger in the right conditions. One of the most distinguishing features of the D. squarrosa is the ferns trunk which retain the hard black bases of the old frond stalks forming a distinctive slender trunk. D. squarrosa like D. fibrosa often forms a ‘skirt’, or ‘investment’ of dead fronds around the top of its trunk. The may not be aesthetically pleasing to some but it plays an important role in maintaining the moisture level at the top of the trunk which may be more exposed to the elements and therefore dry out faster. Your tree ferns will be happiest if you leave old fronds on the trunks until they have turned brown and crispy and the plant has taken back all the goodness stored in the fronds, even then it is best to leave the old fronds on!
The condition in which D. squarrosa thrives is in filtered sunlight, loose well drained soils with lots of organic matter and plenty of water. This species needs an almost constant supply of moisture to its trunk, therefore it is best planted in a sheltered corner where the humidity can be maintained. During the hotter months watering must be done both in the morning and evening, it is also beneficial to the plant to leave a bowl of water directly under the trunk to try and maintain the humidity as high as possible.
D. squarrosa plants should never be brought as bare rooted trunks in the UK, as the chances of the plant surviving are very low. Prior to planting the give your D. squarrosa a good water, it may also be a good idea to let your plant acclimatise in its new position if the plant ahs previously been kept indoors by leaving it outside during the day and bringing it in over night. This will ensure the plant does not go into shock.
Once you are ready to plant your tree fern dig a hole several times bigger than the root system and fill it with a mixture of 2 parts ericaceous compost, 1 part sharp sand, 1 part well rotted leaf mould and a hand full of fish, blood and bone. Once planted make sure the trunk is kept well watered. It is possible for the trunk to grow up to 2ft a year in the right conditions!
The main thing to remember with D. squarrosa is water, water, water! Apart from this the plant will benefit from a good layer of leaf mulch around the roots all year, as well as a weekly feed from spring until the end of summer using a ‘complete fertiliser’ at a very diluted concentrate. During the spring the plant will benefit from a hand full of a slow release fertiliser such as fish, blood and bone or chicken pellets from being scattered sparingly around the roots.
It may be possible to keep this fern outside in the warmest parts of the UK if it is well protected, but anywhere that sees temperatures drop below -4°C (25°F) regularly in the winter months should consider bring the plant under cover, into an unheated greenhouse or conservatory. If this plant is well wrapped and left outside the plant will still need a constant supply of moisture and good air circulation otherwise the plant will rot.
If your plant does not make it through the winter, then do not give up. This plant often sends out underground rhizomes that produce new plants, in the wild D. squarrosa can quickly establish vast colonies.
Family Name: Dicksoniaceae.
Common Names: Slender Tree Fern
Position: Partial to full shade.
Soil: Humus-rich, neutral to acid soil.
Growth Rate: fast.
Eventual spread: 4m.
Max Height: 7m (4m Cultivated).
Hardiness: Half Hardy – they are hardy down to -4°C and the foliage is hardy to -2°C.
Winter tips: Bring plant into unheated green house or conservatory.
Summer tips: Keep trunk almost constantly wet, in a sheltered corner, feed weekly.