Cold-Hardy Palms for Temperate European Landscapes

David A. Francko, Professor and Chair, Botany department, Miami University, Oxford, OH 45056 (franckda@muohio.edu)
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., summer 2002.
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 very wet.

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 F 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 ).

References

Francko, D.A. 2000. Effect of microclimate variation on cultivation of cold-hardy palms in Southwestern Ohio. Palms 44(1):37-46.

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 Issue:12-15.

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.

 

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