Ferntastic!
With leaf blades that can grow to 2.5m and a cinnamoncoloured trunk, the dicksonia tree fern will give your garden an exotic feel, says Monty Don
AFEW weeks ago I planted the first tree fern to grace my garden. It felt like a daring move on a number of accounts. Tree ferns are quite a leap in style and are also expensive, so unless yours looks exactly as you want it to in the garden, it can be a costly mistake.
For about ten years from the mid-90s tree ferns were all the rage and used very much as ‘architectural’ plants, meaning that one or two would be strategically positioned to frame a view or create a viewpoint. This did not stop them being beautiful and fascinating but was both deliberately exotic and actually quite out of kilter with the way that tree ferns grow naturally.
I am lucky enough to have lain on my back in a tree fern forest in New Zealand under the beautifully soft green light that they create. In that mild, temperate and very damp climate the tree ferns grow taller than anything you might see in the northern hemisphere with the trunks permanently in shade and a canopy of fronds overlapping to create the spangled light, which falls softly to the forest floor. It is a kind of green heaven and as far removed from any kind of architectural, trophy planting as might be imagined. I have therefore planted mine at the back of the pond among a number of very tall shuttlecock ferns (matteucia) so it is only visible by looking through the surrounding planting. The aim is for it to enhance and blend with the surrounding growth.
There are hundreds of different tree fern species but very few are possible to grow outdoors in this country. By far the most reliably hardy – albeit with winter protection – is Dicksonia antarctica, and that is what I have planted in my own garden. It originates from Tasmania and has very long leaf blades – up to 2.5m – and a thick cinnamon-coloured trunk.
As with all tree ferns this ‘trunk’ is in fact a bundle of vertical rhizomes surrounded by a bristly padding of roots that are exposed to the air. The roots that grow from the base of this stem are very small and will not be large enough to anchor it into the ground. For this reason you should bury 10-15cm of the trunk in the ground when you plant it and tread it in very firmly.
This fern grows very slowly indeed – no more than 3cm a year – so buy the largest dicksonia you can afford and accept that how it looks immediately after planting is to all intents and purposes how it will look in ten or even 20 years’ time.
It likes to be in partial shade and although it needs good drainage it prefers to be constantly humid. In hot, dry weather it will need spraying at least once a day so that the external roots on the trunk are thoroughly wet. If you do not have a hose with a spray – which would probably be a sensible investment if you buy a tree fern – then pour a can of water into the top of the trunk at the point where the fronds grow out. The trunk will soak up the water like a sponge.
This inverted cone is the most vulnerable part of the plant in cold winters. The best way to protect it is to stuff it with straw and fold the leaves back over it, tying them together like a bonnet. This will act as insulation against the cold and keep the top of the trunk from filling with water that can then freeze, expand and kill the fern. With this protection your dicksonia will be able to withstand temperatures down to 10ºC, especially if it is also protected from drying winds.