Posted on | August 16, 2008 | No Comments
Until the latter part of the 20th century prehistoric tree ferns were rare in the British Isles, apart from some of the well-known stands in Cornwall and other southerly parts of England and of course ‘Inverewe Gardens’ in Scotland where they are bathed in the winter by warmth from the Gulf stream and where I first encountered these majestic giants of the fern world some 35 years ago.
Today species like Dicksonia antarctica are readily available at most of the larger garden centres including some of the well known DIY stores, with several other species available from specialist nurseries across the country.
They add a truly exotic feel to the garden with their superficially palm-like fronds, giving strong shape and stately form to shady, tranquil parts of the garden in dappled shade. They also have a very alluring primitive appearance, as these enormous ferns were around at the time of the dinosaurs.
Tree ferns are native to the tropics and subtropical parts of the southern hemisphere, though several grow well in our cool maritime climate if sited well. They have a vertical trunk-like rhizome (often reaching a great height) from which the fronds emerge, varying in size and proportion from species to species. These trunks are not dead, as I have heard them described by some British gardening TV personalities – they are very much alive, transporting moisture and nutrients from the ground to the fronds.
The fronds are held at the trunk tops in a radiating or spreading fashion, unfurling over many weeks from the crown at the trunk top where all the new growth arises. These new fronds are often called croziers. Unlike trees, if the crown is removed or destroyed, they will not re-grow from the trunk and will subsequently die.
On many species, such as Dicksonia antarctica, the trunks are covered in a thick mass of roots, while other species like Cyatheas, have trunks that are more solid, almost woody, forming fewer roots above ground level, though they are often covered in fine hairs and old frond bases. All tree ferns have small roots that do not thicken like other plants. Most of the tree ferns obtained in the British Isles are produced from land clearance in the southern hemisphere and shipped as cut trunks. When imported, they arrive as sawn off trunks (or large cuttings) that will produce new fibrous roots from the base when planted.
They do not thicken like other plant root systems, staying quite thin and wiry. Sometimes they have already been planted in containers where they have subsequently rooted, though they tend to be more expensive when bought this way. They can also be obtained fairly cheaply as young trunkless plants if you don’t mind waiting a few decades for a decent trunk. As they are such slow growers though, it is advisable to purchase them at a size required to suit your garden. These denizens of the southern hemisphere look good when planted in groups of different sizes, giving a more natural appearance and creating a microclimate which they prefer.
As they are imported fairly dry to make them considerably lighter during transportation, they need to be re-hydrated by soaking the trunk. Always look into the crown to see that there are plenty of new frond buds ready to emerge, especially if they as yet have no fronds. They all prefer a humid atmosphere, benefiting from regular misting in hot or windy weather, or by using a timed watering system that very slowly dribbles onto the side of the trunk, just below the crown. If left to become bone dry, they will only produce inferior fronds in subsequent years, and may even die. For the price you have paid for your new acquisition it would be a rather expensive loss! They deserve to be treated well and will subsequently reward you handsomely with lush growth and years of pleasure and great majesty. Though there are many species of treefern, the most commonly available is the aforementioned Dicksonia antarctica which is in a genus of about 20-25 species of evergreen or semi-evergreen ferns indigenous to Tasmania and north to Queensland. My oldest D. antarctica has been in the ground for nearly 20 years with no protection, taking lows of at least -10C (14F).
In Martin Rickard’s garden in central England, this impressive fern has survived a similar period with protection down to a chilly -15C (5F). Tucking a handful of straw into the crown will protect your valuable plant from the worst frosts. Wind desiccation is probably the most damaging; hence a sheltered corner protected from the prevailing winds is essential. If you feel like being slightly more adventurous there are two other Dicksonias worth considering Dicksonia fibrosa and Dicksonia squarrosa, both indigenous to New Zeeland. The former is commonly known as the Golden Treefern or Wheki-ponga.
The species name fibrosa, refers to the matted roots that make up the fibrous trunk. This is a relatively small and slow growing species of Dicksonia with a thick gold-brown fibrous trunk, found in fairly cold areas at elevations up to 823m (2,700ft), where it reaches a height of up to 6m (20ft), though much smaller in cultivation. Its fronds closely resemble D. antarctica, though shorter at 5-2m (5-7ft), with dark green, bipinnate-pinnatifid, lance-shaped with hairy leaf stalks brown when mature. It also has a rough texture to the upper surface of the frond caused by the upturned edges of the pinnules. It prefers a cool, moist, shaded environment on humus-rich soil.
It is almost as hardy as D. antarctica, taking lows down to about -9C (16F) for short periods, and lower with protection, preferring full to dappled shade. Dicksonia squarrosa, also known as Rough treefern, Hard treefern, Wheki in its native New Zealand, is a suckering tree fern with a delicate appearance. The upright stem produces side crowns up the trunk, as well as underground runners producing side shoots, when mature. It is faster growing than other Dicksonias – up to a height of 8m (25ft) in the wild, though much smaller in cultivation. It prefers humus-rich, well-drained, moist soil in a humid, sheltered location, with plenty of water in the growing season.
Never let the trunk dry out. It is hardy to about -5C (23F) for short periods, and lower with protection. There are many other tree ferns worth considering if you want to start a collection, though for a beginner Dicksonia antarctica is the most commonly available and easiest to grow. As Ferns are such a fabulous range of plants I will be discussing some of many other ferns that are available in next week’s article. On a completely different note, two of the Agaves are flowering at the Exotic Garden and one in particular, Agave filifera is now sporting a (17ft) spike and is a must to see as they are infrequent bloomers in this country, especially outside as these are.