COLD-HARDY TREE FERNS
Introduction and acknowledgments
Tree fern cold-hardiness and climate adaptability
Tree fern cultivation
Winter protection for tree ferns
Treefern internet discussion group
GENERA OF HARDY TREE FERNS:
Lophosoria, Sadleria, Thyrsopteris and Todea
Miscallaneous fern photo gallery
Links to more about ferns and tree ferns
Sources for tree ferns
Hardy Eucalyptus Page | "My Plants" Page
Welcome to my hardy treeferns page! I made this page as a source of information for those of us in USDA zones 9a or colder about how to grow tree ferns.
I don't know about you, but I think treeferns are quite exciting! Giant, primeval-looking fronds atop a tall trunk recall an era of dinosaurs and volcanoes and carboniferous swamps. Not only that, but they also give a very tropical feel to the landscape and make any front lawn feel like Hawaii. And, since they are, after all, ferns; they still blend well with woodland plants and other ornamentals.
Treefern characteristics and morphology (structure)
I have tried not to make this too technical, but I have underlined some words that will come up later in the page.
Please note: "treeferns" are not to be confused with ferns that grow in trees!!! These are called "epiphytic ferns" and are usually small, found commonly on mossy trees in rainforests. (Some even grow on treefern trunks!) A "treefern," on the other hand, actually is a tree in and of itself! (See picture.) Technically speaking, however, they are not real trees, because true ferns do not develop a woody trunk that functions like other trees. All ferns have a rhizome, from which the fronds emerge. These rhizomes can vary (from species to species) from long to short, or be creeping along the ground, or inconspicuous, and so forth. A tree fern is simply a case of the rhizome being very long and strong enough to support itself.
Leaves of all ferns, including treeferns, are referred to as fronds (see picture). On treeferns, the fronds are held at the top of the plant in a spreading manner. They form by uncurling from the crown in the center, which is at the top of the trunk. (This terminology can be slightly confusing, since "crown" is often used loosely to mean the entire top of the plant, including the fronds. Also, with other plants, "crown" may mean something different still.) The crown might be considered the most important part of the plant, since that is where all the leaf growth comes from. If it is destroyed, no more croziers will emerge from it, and the rest of the plant will eventually die.
The frond bases, where they join the top of the trunk, are called stipes; and the fronds when they first begin to emerge and uncurl, and look like a snail's shell, are called croziers. The process of croziers uncurling and expanding to form fronds is really fascinating to watch, and makes tree ferns a lot of fun to grow. Usually it takes several weeks for the expansion of a crozier into a frond to be completed.
Picture of crozier (top) emerging from
crown (bottom). Note also the stipes of older fronds.
Picture of many croziers emerging from crown.
The trunk, really a very long upright rhizome, is the part which supports the crown and fronds. Its main roles are to elevate the fronds above competition from surrounding plants, and to transport water and nutrients to and from the fronds and crown. On many spcies, such as Dicksonia antarctica, the trunks are covered in a great mass of roots. Other species, parcticularly Cyatheas, have trunks of a more solid, almost woody substance and form fewer roots above ground level. The roots of all treeferns are small and do not thicken with age as do the roots of woody plants. A few treeferns form underground buds and can even send up runners some distance away from the parent. Such plants are able to recover if the main crown is destroyed, since essentially they have more than one crown.
All treeferns reproduce from spore. The spore develop in structures called sori on the undersides of the fronds. They are found only on mature plants, and when they are released they look like dust. The main method of treefern propagation is to raise them from spore. It takes most species 5 to 20 years before they are old enough to reproduce.
Where cold-hardy treeferns grow
There are perhaps nearly a thousand treefern species which grow chiefly in the Southern Hemisphere and the tropics. Many of these are quite cold-tender and will suffer if the temperature drops below freezing. But a few from Australia, New Zealand, Africa and some other places are cold-hardy enough to adapt to a less hospitable climate. The list of species on this page is by no means all-inclusive. In addition to these there are probably a number of other species and hybrids that are less well known but could grow in cooler climates. There seems to be a lack of information about tree fern species from South America and Mexico, some of which could be very promising for cool climates. The high Andes, where treeferns thrive up to 14,000' above sea level, and southern Brazil are especially promising places.
The two main genera of hardy tree ferns are Cyathea and Dicksonia. Species of Dicksonia are readily identified by hairs growing on the newly emerging fronds (see photo), and the most common Cyatheas can be identified by the presence of scales on many (but not all) species (see photos: brown scales, white scales). Just because one has scales and one has hairs does not mean that one is a male and the other a female (as one of the contributors to this page was once told by a supposedly qualified nurseryman)! Cyathea formerly consisted of several genera, including Alsophila, Hemitelia and Sphaeropteris. Although they have since been joined, clear distinctions between each group are obvious, and some still regard them as subgenera.
The remaining genera of treeferns are Cibotium, Cnemidaria, Lophosoria, Metaxya, Nephelea, and Trichipteris. Of these, the genera not covered on this page do not contain any cold-hardy species that I am aware of. Of course, more information on this is always welcome! In addition to the true treeferns, there are also some species of Angiopteris, Blechnum, Ctenitis, Culcita, Diplazium, Dryopteris, Leptopteris, Marratia, Polystichum, Sadleria, Thyrsopteris, and a few other ferns that have been known to form at least somewhat of a trunk, but not a large enough trunk to qualify as a real treefern (although I do cover a couple of the hardier ones).
This page would not be nearly so captivating without contributions from the following people. Thank you to Scott Ridges in Bendigo, Australia for a great number of the photos on this page, as well as a considerable bit of the more interesting information. Many thanks to Ralph Booth for photos of some of tree ferns in New Zealand. Keith Rogers has also given me much valuable information and some pictures. I am indebted to Judith Jones of Fancy Fronds Nursery for some of the cultural information. Thank you to Paul Spracklin for a bit of help with details and suggestions for a few other species I would not otherwise have thought to include. Thank you to Peter Richardson for use of many of his photos. And thank you to Imtiaz McDoom-Gaffoor for information and articles about tree ferns in Britain. Thanks also to Les and Rosemary Vulcz, David Pruitt, Neville Crawford, Alistair Wardlaw, Ed Brown and Martin Rickard for various tidbits of information, photos and/or spore!
Finally, since much of this information is based on what I have heard or read rather than my own experience, I invite you to inform me about any errors on the page or misunderstandings I may have generated.
GENERA OF HARDY TREE FERNS:
Blechnums will be dealt with in brief since they do not fall into the category of "true" tree ferns.
A relatively small genus of magnificent tree ferns from Central America, Hawaii and Southeast Asia; not formerly included because they are generally not particularly cold-hardy. However, I did recently hear about someone overwintering the spectacular Hawaiian C. menziesii in the cool climate of Britain, and so decided this genus deserved a little more attention. Cibotium is closely related to Dicksonia.
This is by far the largest genus of tree ferns, containing over 800 species. Many are strictly tropical, but some come from temperate areas cool enough that they can be grown in more extreme climates. Even some of the tropical ones seem remarkably adaptable to temperate climates with light frosts, and cold-hardiness limits have not yet been found for some of these. Compared to Dicksonia, the most common Cyathea species generally grow faster when young, and, in my opinion at least, they are a bit more on the primitive-looking side and not quite so woodland-ish (although the Dicksonias are actually more primitive). Considering the sheer number of species in existence, it is possible that the following small handful listed are only a fraction of those that could be grown in cool climates. Those belonging to the Sphaeropteris group can be distinguished by their thick, fleshy stipes; in contrast to the smaller, woody stipes of the Alsophila group.
Cyathea X marcescens
This genus is most easily distinguished from Cyathea by usually having fronds of a more stiff, leathery substance, and the absence of scales on the croziers as mentioned previously. The individual fronds are more convex when viewed from the top, as opposed to the often flat fronds of many Cyathea species. There are also important distinguishing features on the reproductive structures. Some species, especially D. antarctica and its close relatives, can take on sort of a "shuttlecock" or "vortex" appearance, as if all the fronds together are like a funnel, with the crown at the center. By far the most common Dicksonia encountered in cultivation is D. antarctica, the Tasmanian Tree Fern. D. fibrosa, a species from New Zealand, is sometimes sold as and mistaken for this species in California. There are also several cold-tender tropical species of Dicksonia, making about 25 species all together.
Lophosoria, Sadleria, Thyrsopteris and Todea
Like Blechnum, these are not classified as true treeferns, but they do form trunks or very large rhizomes that suggest treefern like characteristics.
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Background image is Cyathea smithii, photo courtesy of Peter Richardson.
Last modified December 8th, 2002
Page compiled and maintained by Ian Barclay