Cold Hardy Highland Palms

by Ian Barclay, Olympia, Washington, USA
Chamaerops No. 43-44, published online 05-08-2002

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Picture 1: Caryota maxima "Himalaya" in its mountaineous habitat in northeastern India.
Picture 2: Arenga micantha in the remote foothills of the eastern Himalayas.
Picture 3: Parajubaea torallyi var. torallyi is a popular ornamental in Bolivia.
Picture 4: Ceroxylon parvifrons high up in the Andes in Ecuador.

While many palm species popular in California are rapidly becoming better known in the Pacific Northwest, one important group of potentially hardy palms remains largely forgotten. This group is the highland palms. A few are discussed in old books and articles, but they have been very slow to make their way into cultivation and remain shrouded in mystery. I would like to consider the geography and climate of their natural habitat, look at a few of the species that are starting to become better known, and examine their potential for cultivation in the Pacific Northwest.

'Highland palms' are a rather loosely defined group of palm species that inhabit high mountainous areas. They grow exclusively in mountain ranges in the world's tropical or subtropical regions. Since these mountainous areas are significantly cooler than the steamy tropics beneath them, palms from these regions will grow well under cool moist conditions.

The species that grow closest to the equator, however, are not accustomed to seasonal change and must be somewhat adaptable to thrive in cultivation. Mountain ranges farther from the equator have more seasonal variation in rainfall and temperature and are therefore more likely to contain species that will perform well in lowland temperate climates such as ours. In the Pacific Northwest they are likely to be best suited to cool coastal areas with less seasonal variation in temperature and cloud cover.

Highland palms remain largely unknown in cultivation for at least two reasons. Probably the main reason is their inaccessibility, as many are found in some of the world's most remote and difficult-to-reach places. Many dwell on steep cliffs or in areas where roads are poorly developed or nonexistent, necessitating multiple day trips or special equipment for seed collecting. Special permission from host countries' governments may also be a challenge. Few people will bother to trek up into the mountains in some far-off country to search for an isolated grove of palms, or to bring back seeds should they be fortunate enough to find some. A second reason highland palms remain rare in cultivation is that there are few places in the world where a large population exists in combination with a climate where they will thrive. The San Francisco Bay area is one exception: the climate there is comparable to tropical and subtropical mountain ranges, and some highland palms are being tried in this area.
I will begin with the Himalayas, a subtropical mountain range containing the world's highest peaks. The climate in this region is characterized by a consistent seasonal pattern. It is rather dryish and cool in winter and extremely wet in late summer. Although this is the opposite of the Pacific Northwest's precipitation pattern, many species from this part of the world still adapt well here. The constant summer cloudiness in Southeast Asia and the Himalayas keeps the summer temperatures lower than one would expect for such a latitude, enabling many of these plants to tolerate our cool summers.

One truly spectacular palm from the Himalayas is the cold hardy Caryota (Fishtail Palm), recently introduced as C. 'Himalaya' by European palm experts Martin Gibbons and Tobias Spanner. It is actually a montane form of C. maxima. Some years ago it was erroneously introduced into cultivation in California under the name C. urens 'mountain form'. It is single trunked, and, like other fishtails, it has beautiful, bipinnate leaves with sharply serrated edges. It grows in the Himalayan foothills near Darjeeling, India, to an elevation of 8,000 ft., and is also cultivated in Katmandu, Nepal. Martin Gibbons estimates it will be hardy to about -7°C (19°F) as a mature tree. This estimate might be slightly optimistic, however, for all but the best provenances of this species—it will probably not be hardy enough to survive our Northwest arctic blasts, but it would be a fun challenge to try with some protection in the most sheltered microclimates.

More recently, Gibbons and Spanner have discovered a promising unknown Caryota species they are calling Caryota sp. 'Mystery'. It originates from Bhutan northward into the lowest parts of Tibet. It has the habit of suckering to form a clump of short trunks, like the tropical C. mitis. Because of this characteristic, it might be able to reach a large size in the Pacific Northwest between severe winters, and recover if it freezes to the ground periodically, in the same manner as C. mitis in Florida.

Although Caryota is a predominantly tropical genus, it is likely that hardier Caryota spp. may be found in Southeast Asia or the Himalayas in the future. C. basconensis and the Chinese C. ochlandra are somewhat frost tolerant, but probably not enough to be worth attempting in our region. Anyone attempting to grow Caryota in the Pacific Northwest should wait until the palm reaches a fairly large size before putting it in the ground, and water and feed it heavily so that it reaches a large size quickly.

Another promising palm recently discovered by Gibbons and Spanner in Bhutan and southern Tibet is Arenga micrantha. It is not huge but very impressive, characteristically forming multiple trunks. It would probably be at least as hardy as Caryota sp. 'Mystery', and should certainly be a good bit hardier than A. engleri.

Now we shall go to the Andes Mountains of South America, home to many fascinating genera including Parajubaea and Ceroxylon. The climate there is one of perpetual coolness, and, in the north, wetness. Most of the palms in this region are able to tolerate light frosts down to -3°C (27°F), but some of the species that grow at extreme elevations, or south of the tropics towards Bolivia, are likely to be hardier. It will take quite a bit of adaptability if they are to tolerate our arctic blasts and seasonal variations in temperature and cloud cover, though it seems certain they will grow well in cool, wet weather—something we Northwesterners get more than our fair share of. Hot, dry weather is not to their liking, but I doubt this would be a problem in the Pacific Northwest with proper siting and watering.

Ceroxylon is a genus of about a dozen or more large, pinnate-leaved palms. They are known for their white waxy trunks, which in some species can grow to 60 m (200 ft.) tall—the tallest of the world's palms! This spectacular height makes them quite an eerie sight to behold in their native habitat. What's more, Ceroxylon grows at a higher altitude than any other palm. C. utile (now considered synonymous with C. parvifrons, a much smaller species) was once reported to grow at the incredible elevation of 13,450 ft. above sea level in Ecuador. (For comparison, the top of Mount Rainier, near Seattle, is 14,411 ft. high.) Unfortunately, recent attempts to find this elusive high-elevation palm grove were not successful. This report is now believed to be erroneous, but it does not rule out the possible existence of other high elevation stands that have yet to be discovered.

Many Ceroxylon species grow near the equator, and are best adapted to perpetual coolness with no seasonal variation whatsoever. This will probably not be a palm for more extreme inland areas such as the Willamette Valley of Oregon. Some species also grow at lower elevations in warmer rainforests. The most southerly ranging species, and probably the best ones to try in our region, are C. parvifrons, C. vogelianum (syn. hexandrum), and C. parvum. These can be found growing above 9,000 ft. in northern Bolivia. C. quindiense seems at least as hardy as C. parvifrons in my experience, and may also be worth trying. C. alpinum (syns. C. ferrugineum, C. andicola) is not as hardy as some literature suggests, and is actually one of the more heat-tolerant species.

Attempts to grow Ceroxylon in California have been rather unsuccessful overall, but there are some exceptions, especially in the San Francisco area and at the Huntington Botanic Gardens. Evidently they seem to have trouble withstanding the hot, dry summers in most of California, and overall they remain very rare. They are reported to develop dreadfully slowly from seed, remaining trunkless for 20 to 35 years—this is a palm to plant for your grandchildren! Trunk development is very rapid, however, when it finally begins.

Mike Lee of Colvos Creek Nursery on Vashon Island, Washington was one of the first to attempt Ceroxylon in the Pacific Northwest. He reported losing many of his seedlings to heat and drought, and observed that they would only grow while it was cool and rainy. Possibly nothing remains to show for his efforts. However, evidence in California suggests that older, established specimens of Ceroxylon spp. have formidable bud-hardiness, and may be able to recover well from severe frost damage as long as it does not occur too frequently. In addition, one of Mike Lee's C. quindiense survived the December 1990 freeze in the ground on Vashon Island! (This palm was eventually dug up and moved to Mexico.) Others have tried to grow Ceroxylon in the Pacific Northwest and failed, losing them to winter cold soon after planting. But until we grow one to trunk-forming size, I do not think we can get an accurate feel for their hardiness. It has been suggested that bringing the daytime highs above freezing would help them endure our worst winter cold.

Parajubaea is very striking in appearance, and has been described by some as looking like a coconut palm. Although related to the slow growing Jubaea chilensis (Chilean Wine Palm), they fortunately seem much faster growing than both Jubaea and Ceroxylon. Repeated efforts to introduce Parajubaea cocoides to the San Francisco Bay area from Quito, Ecuador, where it is common, have been hindered by problems obtaining stock. This species is found at 7,300 to 9,700 ft. above sea level in Ecuador. A few Pacific Northwest gardeners have tried it, and found it hardy to about -4 to -5°C (the mid-20s F) as a young plant, though older specimens in California have recovered from temperatures as low as -9°C (16°F) in 1990.

Another species, P. torallyi, grows at the amazing altitude of 8,700 to 11,100 ft. in Bolivia. It is more cold hardy than P. cocoides, but unfortunately it is extremely scarce. This species has two distinct varieties, var. torallyi and var. microcarpa, of which var. torallyi is the larger and more vigorous. It has been introduced to Australia and southern Europe, but so far only two small plants are to be found in California. Because Bolivia is far enough south to have a more seasonal climate than the deep tropics, P. torallyi may prove very well adapted to the Pacific Northwest if it is hardy enough. Small seedlings have withstood -7°C (19°F) with only light to moderate damage in Italy. Despite growing in very dry areas of Bolivia, it has proven very tolerant of moisture in California. A third species, P. sunkha, is found at lower elevations in Bolivia, and is fairly similar to P. torralyi var. microcarpa. Seed of all four forms has recently been introduced into cultivation, so there should be more plants available to try in the future.

All Parajubaea spp. have a very vigorous, deep taproot system, and are probably not suited to long-term pot culture. If you are fortunate enough to obtain seeds, planting them in too shallow a pot is likely to stunt the growth of the plant. Like the other palms mentioned here, Parajubaea should be given careful winter protection for their first few years. They are likely to be more tolerant of our dryish summers than Ceroxylon. They may also hybridize with Jubaea in cultivation, which could make for some interesting future hardy palm possibilities.

So, when will we see these palms towering over our gardens and cities? These palms are only now being tested by pioneering palm growers and hobbyists, so no conclusive data will be available for many years. Some will not be fully hardy and will probably never be suited to widespread cultivation in the Pacific Northwest. The south coast of Oregon may give many highland species the protection from Arctic blasts they need for long-term survival. Others may find their microclimate of choice on islands in Puget Sound or the Strait of Georgia. Some may be completely hardy and adaptable throughout western Washington, Oregon, and southwest British Columbia. Some may fail completely. Perhaps one will someday replace Trachycarpus fortunei as our most popular hardy palm.

In any case, the presence of these and other remarkable palms ensures many years of excitement ahead in the realm of cold hardy palm cultivation. Future years promise the continuing discovery of 'new' highland palm species, and continued introduction of species that have not been cultivated in our region before! We have only scratched the surface with the species we have been able to obtain so far.

Reprint from the Hardy Palm International.

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