THE DESERT NORTHWEST - Cold Hardy Highland Palms

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Cold Hardy Highland Palms

This article first appeared in Hardy Palm International, Edition #51, August 2002.

While many palm species popular in California are quickly catching on 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 many 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 come exclusively from mountain ranges in the world's tropical or subtropical regions. Since these mountainous regions are significantly cooler than the steamy tropics, palms from here are best adapted to cool moist conditions. The species that grow closest to the equator, however, are not accustomed to seasonal change; requiring them to 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.

Ceroxylons at San Francisco Botanic Garden.
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 places. Many of these palms dwell on steep cliffs, or in areas where roads are poorly developed or nonexistent, which necessitates multiple-day trips or special equipment for seed collecting. Special permission from other countries' governments may also be a challenge to obtain. Few people will bother to trek up into the mountains in some far-off country to search for an isolated grove of palms, and bring back seeds should they be fortunate enough to find some. A second reason they remain unknown in cultivation is that there are few places in the world where a large population exists in combination with a climate where highland palms will thrive in cultivation. The San Francisco Bay area is one exception: the climate there is reasonably 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. Winters are typically cool and rather dry, but the weather turns extremely wet in late summer with the onset of the monsoon. Although this is the opposite of the Pacific Northwest's precipitation pattern, many plant 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 introduced to cultivation under the name C. urens 'Mountain Form' to California. It is single-trunked, and, like other fishtails, it has beautiful, bipinnately compound leaves with sharply serrated edges. It grows in the Himalayan foothills near Darjeeling, India, to an elevation up to 8,000'; and it is also cultivated in Katmandu, Nepal. Gibbons estimates it will be hardy to about 19°F as a mature tree. However, this estimate might be slightly optimistic 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. Experience thus far has demonstrated that young plants are not very hardy at all, and may be killed by moderate frosts.

This palm at the Los Angeles County Arboretum in
Pasadena, California is labeled 'Darjeeling Extra Hardy'.
It is probably a form of C. maxima, and quite likely the
same plant that goes by the name C. maxima 'Himalaya'
and C. urens 'Mountain Form'.
More recently, Gibbons and Spanner have discovered a promising unknown Caryota species they have given the provisional name 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 possible that more Caryota species with some hardiness may be found in Southeast Asia or the Himalayas in the future. C. basconensis and the Chinese C. ochalandra are somewhat frost tolerant, but probably not enough so 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 will reach 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, which has been attempted by a few brave Northwest gardeners.

Now we shall go to the Andes Mountains of South America, home to many fascinating genera of palms including Parajubaea and Ceroxylon. The climate there is one of perpetual coolness, and, in the north, and on the east side of the mountains, wetness. Most of the palms in this region are able to tolerate light frosts down to about 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 on their part if they are to tolerate our Arctic blasts and seasonal variations in temperature and cloud cover. However, it seems certain that 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.

A young Ceroxylon at the Oakland Bay Palmetum. I
didn't have anything with me to use for scale except
my wallet: as you can see, the petioles and leaves on
this pre-trunking plant are enourmous!
Ceroxylon is a genus of a dozen or more large, pinnate-leafed palms. They are known for their white waxy trunks, which in some species may reach 200' 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' above sea level in Ecuador. (For comparison, the top of Mount Rainier is 14,411' high.) Unfortunately, recent attempts to find this elusive high-elevation palm grove have not been 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. C. hexandrum) and C. parvum. These can be found growing above 9,000' in northern Bolivia. Of these, C. vogelianum has shown itself to be the most tolerant of some frost and difficult conditions for me. 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, originating at a lower altitude.

Until recently, most attempts to grow Ceroxylon in California were rather unsuccessful. However, some plants have flourished for a long time 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, typically remaining trunkless for 15 to 25 years - this is a palm to plant for your grandchildren! However, trunk development, when it finally begins, is very rapid, as much as 5' per year has been recorded in New Zealand.

Ceroxylon parvum at UC Berkeley Botanic Garden,
California. This may be one of the hardiest Ceroxylon
species to frost.
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, as I am unaware of any surviving Ceroxylon plants in Northwest gardens. 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 landmark freeze of December 1990 in the ground in a Vashon Island garden. (This palm was eventually dug up and moved to Mexico by its owner.) Others have attempted 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 artificially bringing the daytime highs above freezing would help them endure our worst winter cold.

Parajubaea species are also very beautiful palms, and has been described by some as reminiscent of the tropical looking coconut palm (Cocos nucifera). Fortunately for gardeners, although related to the slow-growing Jubaea chilensis (Chilean Wine Palm), they 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 resulted in it being available from some nurseries, though scarce. This species comes from about 7,300 to 9,700' above sea level in Ecuador. A few Pacific Northwest gardeners have tried it, and found it hardy to about the mid-20s F as a young plant, though older specimens in California have recovered from temperatures as low as 16°F in 1990.

Parajubaea cocoides at UC Berkeley Botanic Garden,
Another species, P. torralyi, grows at the amazing altitude of 8,700 to 11,100' in Bolivia. It is more cold-hardy than P. cocoides, and remained extremely scarce until a few years ago. Now, it is far from common, but a few California nurseries do carry it. This species has two distinct varieties, var. torralyi and var. microcarpa, of which var. torralyi is the larger and more vigorous. The var. microcarpa, however, may be a little hardier to cold. Because Bolivia is far south enough 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 19°F with only light to moderate damage in Italy; however, I did not get quite such good results in my garden. Despite growing in very dry areas of Bolivia, it has proven very moisture tolerant in California. A third species, P. sunkha, is found at lower elevations in Bolivia, and is fairly similar to P. torralyi var. microcarpa.

All Parajubaea species 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 trialled 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. If we're really lucky, a few 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!

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