Cold-Hardy Palms for Temperate European
David A. Francko, Professor and Chair, Botany department, Miami University, Oxford,
OH 45056 (email@example.com)
Chamaerops No.48 - published online 24-05-2004
- Top left: Dwarf palmetto (foreground), needle palm (left rear) and southern magnolia 'Little
Gem', Upham Palm Court, Miami University campus, Zone 6a, November 2002.
- Top middle: Same plot in January 2003
- Top right: Dwarf palmetto (S. minor)
- Bottom: Chamaerops humilis (Mediterranean fan palm), Upham Palm Court, Miami University campus, Zone 6a.,
Photos: David A. Francko
- Top left: Washingtonia filifera (California fan palm), Upham Palm Court, fall 2002.
- Top middle: Foliage and flowers of southern magnolia (M. grandiflora; 'Brackens Brown Beauty'),
author's home landscape, Oxford, OH, Zone 6a.
- Top right: Crape Myrtle 'Acoma' (white flowers) and 'Tonto' (magenta flowers) in front
of 'Edith Bogue' Southern Magnolia, near Pearson Hall on the Miami campus, Zone 6a.
- Bottom left: Gold Dust Plant (Aucuba japonica 'variegata'), Cox Secret Garden, Miami University
campus, Zone 6a.
- Bottom middle: Phyllostachys aureosulcata var. aureocaulis near Pearson Hall, summer 2002
- Bottom right: P. nigra (black bamboo)
Photos: David A. Francko
Palms, Bougainvillea, Oleander, and other subtropical ornamental species are landscaping mainstays
in warm-winter areas of Europe and define that "Mediterranean look" known around the world. But if
you live in colder areas where winter temperatures frequently drop well below freezing, you may believe that
these warm-climate ornamentals are beyond your reach. After all, everyone knows those things won't grow
here! But conventional wisdom about what will and will not survive and even thrive in cool-to-cold-winter parts
of Europe (approximately USDA Zones 6 through 8a) is incomplete at best and sometimes flat wrong. For example,
although most of the world's roughly 1500 palm species are tropical or subtropical in their distribution,
at least 100 species easily survive freezes down to 20°F (-7°C), and a surprising number will even survive
occasional bouts of sub-zero Fahrenheit (below 18°C) cold (Gibbons and Spanner 1999; Francko 2000;
Francko and Wilson 2001: Francko and Wilhoite 2002)!
In Palms Won't Grow Here and Other Myths: Warm-Climate Plants for Cooler Areas (Timber Press; 2003), I
document more than 300 woody and non-woody warm-climate ornamentals that survive at least 0°F (-18°C),
in the ground all year round, with minimal winter protection. These include palms, other broadleaved evergreen
trees and shrubs, deciduous flowering species such as crape myrtles, bamboo, cacti, agaves, and temperate bananas.
The book describes how to evaluate your landscape's microclimates, how to integrate warm-climate species
into an existing temperate landscape, and which cultivars work best under your conditions.
The take-home lesson of my book is simple: even if you live in a cold-winter area, your landscape can have the
bold variety in form and function associated with warmer climes. So, if you want to create a 'tropical
looking' paradise in your temperate yard or merely want to incorporate a palm or other dramatic specimen
planting to an existing landscape, go for it! To get you started, here's a capsule description of some
(but by no means all) of the palm species that are adaptable to colder European climates as well as traditional
Palm Country, in roughly descending order of cold tolerance.
When purchasing palms, it's best to acquire larger containerized or balled-and-burlapped specimens with
dense root balls. The palms below may be grown in any soil type. Watch for drought stress during the two to
three year establishment period, and modest winter protection is a must most years for best foliar overwintering
(heavy mulching/antidessicant spray). Hardiness information below is for established plants. The hardiest of
the cold-hardy palms are clump-form, meaning that they form at best a short trunk, but several true palm trees
are very cold tolerant as well.
Needle Palm (Rhapidophyllum hystrix): Hardiest clump forming palm, no damage to 18°C (0°F)
even in first year specimens, although spear leaves are sometimes killed. Survives 30°C (-22°F)
with defoliation; grows slowly to perhaps 2.5 m tall/broad in Zone 6b; native to SE USA (Figs. 1a, b and 4).
This palm is as hardy as the southern magnolias and tree hollies, but best out of direct winter wind/sun. Partial
sun to full sun but will take some shade. Exceptionally beautiful deep-green leaves with gray-green undersides.
In areas with cold but dry winter climates, try the Mazari Palm (Nannorhops ritchiana), a Middle Eastern native
that may rival needle palms under such conditions.
Dwarf Palmetto (Sabal minor) and Louisiana Palmetto (S. "Louisiana"): Many varieties and putative
ecotypes; second most hardy palm, little leaf burn down to 0oF, defoliates somewhere between 5° and
10°F, but has underground bud tissue recovered down to 31°C (-24°F) in Wichita, Kansas.
Slow grow to perhaps 5 ft. tall and broad in Zone 6 (Figs. 1a,b and 3). Any relatively sheltered site, even
Windmill Palm (Trachycarpus fortunei / T. takil): Probably hardiest tree palm; survived 26°C
(-14°F) with defoliation in our experiments, with leaf burn beginning about 13°C (-8°F), and
major defoliation around 18°C (0°F), but basal parts of most leaves remain green well below zero
F. In winter, protect the trunks and foliage with heavy leaf litter to add several degrees of hardiness and
help keep water out of crown cavity in winter. Ideal choice for cool marine climates; large specimens grace
coastal British Columbia, Canada and the British Isles. Tolerates heavy soils, full sun to partial shade.
Cabbage Palmetto (Sabal palmetto) and related species: The State Tree of Florida and South Carolina may
ultimately prove as hardy if not more so than windmill palms! This is the 'real' palm tree, familiar
to everyone who visits the Florida peninsula or the Caribbean. In our Ohio experience (Fig. 3) and that of enthusiasts
in Zone 6 parts of the Cumberland Plateau of Tennessee, leaves undamaged down to low single digits F, and some
foliage still green below zero °F (-18°C). Mature, trunked specimens known in Zone 7a/6b, and trees
in these areas frequently survive sub-zero °F temps. Rapid grower; even if partially defoliated will produce
crown of 4 to 5 large fan leaves by summer, so can look more impressive as a juvenile than a mature S. minor.
Takes many years to form a trunk. In cold-winter areas, best to plant large (15 gallon and up) trunkless rather
than transplant trunked specimen. In winter protect like windmill palm. Full sun best and will tolerate saline
soils. Sabal "Birmingham" may prove to be the world's most cold hardy tree palm. Still rare in
commerce. Believed to be a hybrid between S. palmetto and S. minor, an established specimen in Zone 6b Tulsa,
Oklahoma is ca. 3 m tall and broad, has only minimal leaf damage down to 13°C (-8°F) and has survived
-26oC (-14oF). Texas Palmetto (S. mexicana (S. texana)) and Brazoria Palmetto (S. x texensis) also do well in
dryer areas with cool winters.
Mediterranean (European) Fan Palm (Chaemarops humilis): This beautiful, often multi-trunked palm is familiar
to residents around the Mediterranen Sea and in similar climatic areas of the world (e.g., Southern California
and the American South). But this species is also extremely cold hardy, with foliage that is undamaged down
to perhaps the mid-teens F (ca. 10°C); small well-mulched specimens easily survive 18°C
(0°F) or even a bit colder (Fig. 5).
Blue Hesper Palm (Brahea armata) and Chilean Wine Palm (Jubea chilensis): Both of these tree palms, native
to Baja California and cold desert areas of Chile respectively, are relatively hard to find in commerce but
worth the effort, especially in areas that rarely drop below about 10°C in winter. J. chilensis, although
adapted to dry climates, does well in the heavy, wetter clay of the Southeastern U.S.
California Fan Palm (Washingtonia filifera) and Mexican Fan Palm (W. robusta) are ideal for dryer areas
in the southwestern U.S. and climatically similar areas of Europe. W. robusta, despite the name, is less cold
hardy than the California fan palm and defoliates around 9°C (15°F) W. filifera foliage (Fig.
6) will take several degrees more cold, and both species readily survive 18°C (0°F) and even below
with defoliation. As such, Washingtonia is often grown in cold-winter areas as a 'chainsaw palm'.
When foliage dies, cut off dead leaves, spray a little fungicide into the crown cavity, wrap the trunk (especially
the top of crown) to exclude water, and mulch base heavily. In the next growing season you'll delight in
a full crown of 8 to 10 leaves that regrow each season. Trunked specimens up to 2.5 m in height exist in some
Zone 6b areas. An interspecific hybrid called Washingtonia x filibusta is now entering the market and is said
to be more cold hardy than either parent.
Jelly or Pindo palm (Butia capitata): Perhaps the most cold hardy feather-leaf palm species, defoliates
in mid-teens êF but survives much colder temperatures with heavy mulching.
Non-palm companion species: There are literally hundreds of viable woody and non-woody warm-climate plants
that create a tropical look but are in fact cold-winter hardy. I focus here on just a couple specimen plants
that would be on any warm-climate landscaper's Top 10 list.
Southern Magnolia (Magnolia grandiflora): The signature tree of the American South is available in numerous
cold-hardy cultivars suitable for USDA Zone 6 and even colder conditions. The glossy dark green evergreen foliage
with large, fragrant white flowers in late spring through summer cannot be beat (Fig. 7). More than two dozen
cultivars of Crape Myrtles (Lagerstroemia indica) are root-hardy through Zone 5 and provide massive, colorful
blooms from midsummer through frost in full sun (Figs. 8 and 9). Many of these varieties are remarkably cold
hardy, and with care can easily be grown as small trees with exceptional exfoliating bark even in Zone 6. For
shady parts of your landscape try the Gold Dust Plant (Aucuba japonica; Fig 10) or one of the newer cold hardy
Camellia varieties now on the market (Fig. 11) and available via mail order. Finally, no tropical-looking European
garden would be complete without temperate bananas and bamboo. The Japanese Fiber Banana (Musa basjoo) is root
hardy with mulching through Zone 5 and perhaps even colder and reaches almost 3 m in height each growing season
(Fig. 9). Although many cold hardy bamboo varieties are fairly aggressive runners in warm-winter climates, they
are much more easily controlled in cold-winter areas. Try Phyllostachys aureosulcata var. aureocaulis (Fig.
12a) or Black bamboo (P. nigra; Fig 12b ).
Francko, D.A. 2000. Effect of microclimate variation on cultivation of cold-hardy palms in Southwestern Ohio.
Francko, D.A. 2003. Palms Won't Grow Here and Other Myths: Warm Climate Plants for Cooler Areas.
Timber Press: Portland, Oregon, USA and Cambridge, U.K., 308 pp.
Francko, D.A. and K.G. Wilson. 2001. The Miami University Hardy Palm Project. Rhapidophyllum Winter 2001
Francko, D.A. and S. Wilhoite. 2002. Cold-hardy palms in Southwestern Ohio: Winter damage, mortality, and
recovery. Palms 46(1):5-13.
Gibbons, M. and T. Spanner. 1999. Palms in temperate climates. Palms 43(3):91-93.
20-06-13 - 03:53GMT
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