Cold Hardy Highland Palms
by Ian Barclay, Olympia, Washington, USA
Chamaerops No. 43-44, published online
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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
Picture 3: Parajubaea torallyi var. torallyi is a popular ornamental
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 speciesit
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 weathersomething
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.) tallthe 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 yearsthis 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
Reprint from the Hardy Palm International.
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