Palms on the Edge: Species and Strategiesfor Landscape Utilization

Garry V. McDonald1,4, Michael A. Schnelle2,

and Michael A. Arnold3

ADDITIONAL INDEX WORDS. Arecaceae, Palmae, cold temperature tolerance,microclimate

SUMMARY. An emerging niche in landscape design is the creation of exotic venues incommercial and residential settings using unusual plant materials. For instance, thecreation of a tropical looking pool area at a hotel, a southwestern desert look for aMexican restaurant or an oasis for the consumer at a shopping venue can all be inpart achieved by the addition of specific plants. Palms (Arecaceae) can be animportant component of this effort, even in temperate landscapes. This articlefocuses on issues related to the incorporation of palms in temperate landscapes.Although palms are signature plants of tropical regions, a surprising number ofspecies can be grown in U.S. Department of Agriculture cold hardiness zones 8, 7,or colder via a combination of appropriate genotype selection, attention tomicroclimates in design specifications, and/or special cultural practices to mitigatethe impact of cold temperatures. Cold-tolerant palms can be a critical designelement, especially when paired with other lush tropical-appearing plants, to achievethe goal of creating the illusion of an exotic tropical locale in temperate-climatelandscapes. Genotypic and site specification, careful attention to establishmentrequirements, and modified maintenance practices are critical determinants forsuccess that will be addressed.

Palms used in the landscape cancreate a tropical ambiance andare commonly used around

commercial, retail, and private prop-erties in the southern United States,particularly along the coast from Vir-ginia to Texas and in the southwest-ern United States and in many parts ofCalifornia. They are especially popu-lar around swimming pools and sundeck areas at hotels and resorts(Arnold, 2008). Palms are also exten-sively used around many ethnic foodrestaurants, such as those with Mex-ican or Caribbean cuisine, to createan atmosphere indicative of more

tropical areas (Arnold, 2008). Inaddition, many homeowners usepalms in the landscape to lend anexotic feel to backyard entertainmentareas or to stress the southern vernac-ular (Riffle, 1998; Riffle and Craft,2003).

Studies investigating tempera-ture trends in Texas and the south-western United States from the years1941 to 2000 show an overall warm-ing trend post-1970 (Englehart andDouglas, 2003). Warmer wintersassociated with this trend haveencouraged palm plantings away fromthe immediate Gulf Coastal areas intoareas as far north as the Dallas-Ft.Worth metroplex in Texas [U.S.Department of Agriculture (USDA)Plant Hardiness Zones 8a-7b (USDA,1990)] central and eastern Oklahoma(Zones 7a and 7b), central Arkansas(Zone 7a), and across the upper south-ern United States to the Atlanticseaboard. For instance, in CollegeStation, TX, which is listed as USDAZone 8b, plantings of queen palm(Syagrus romanzoffiana) and chinese

fan palm (Livistona chinensis) havebeen used in many commercial land-scape projects, whereas these specieswere once foreign to landscapes out-side of the immediate Gulf Coast orthe Houston, TX, metropolitan areabefore 1990 (G.V. McDonald, per-sonal observations). California fanpalm (Washingtonia filifera) and jellypalm (Butia capitata) have been suc-cessfully planted in northeasternTexas (Zones 7b and 8a) at severalsites since the early 1990s (G.V.McDonald, personal observations).In fact, jelly palm usually exhibitspoor growth in areas lacking distinctcooler winter temperatures such assouthern Florida and the lower RioGrande Valley of Texas (Arnold,2008; Riffle, 1998). Another impor-tant factor in the expanded range inwhich palms are planted is the heatisland effect associated with largeurban areas. Heat islands are highlydeveloped areas that are hotter thannearby rural areas. It has beenreported that the annual mean tem-perature of a city with a populationexceeding one million people can be1 to 3 �C warmer than surroundingareas (Englehart and Douglas, 2003).An even greater effect can occurat night when temperatures can be12 �C higher than rural areas (Oke,1987, 1997).

In addition to the california fanpalm, which is native to isolated can-yons in California and Arizona, otherspecies of palms are indigenous to thesouthern and southwestern UnitedStates and have varying cold tolerance(Table 1). Florida has the greatestvariety of native palm species in theUnited States. (Black, 2003; Little,1977). The needle palm (Rhapido-phyllum hystrix), a native to the south-eastern United States, is listed ashardy to USDA zone 6b (McClendonet al., 2007). Dwarf palmetto (Sabalminor) has a wide geographic distri-bution in the United States withprovenances and recognized horticul-tural variants from coastal North Car-olina to McCurtin and LeFlorecounties of Oklahoma to the hill coun-try region of central Texas (Arnold

UnitsTo convert U.S. to SI,multiply by U.S. unit SI unit

To convert SI to U.S.,multiply by

(�F – 32) O 1.8 �F �C (1.8 · �C) + 32

The authors wish to thank Dr. Brent Pemberton forthe use of his images.

Mention of a trademark, proprietary product, orvendor does not constitute a guarantee or warrantyof the product by the authors or the University ofArkansas, Oklahoma State University, or Texas A&MUniversity, and does not imply its approval to theexclusion of other products or vendors that also maybe suitable.

1Assistant Professor of Landscape Horticulture, 316Plant Science Building, Department of Horticulture,University of Arkansas, Fayetteville, AR 72701

2Professor and Extension Ornamentals/FloricultureSpecialist, Horticulture and Landscape ArchitectureDepartment, 358 AG Hall, Stillwater, OK 74078-06027

3Professor of Landscape Horticulture, Texas A&MUniversity, Department of Horticultural Sciences,207 Horticulture/Forestry Sciences Building, Col-lege Station, TX 77843-2133

4Corresponding author. E-mail: gmcdonal@uark.edu.

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2008; Little, 1977; McClendon et al.,2007; Vines, 1960). The increaseduse in palms grown outside traditionalareas has generated inquiries aboutcold-hardy species, and their manage-ment and incorporation into landscapedesign. This article describes speciesthat are cold hardy to at least USDAZone 8 and gives recommendations onmanagement and cold protection inmarginal climatic areas.

Cold-hardy landscape speciesIt has been estimated that as

many as 100 species of palms willtolerate temperatures as low as 20 �F(Frankco, 2003). Selected palm spe-cies grown in warm to cool temperateregions and their reported cold

hardiness are provided in Table 2(Arnold 2008; McClendon et al.,2007). This species list is not exhaus-tive, but represents palm species thatare being grown commercially andthus available to the landscape indus-try and homeowners. Microclimates,heat islands, or protected areasmay allow some species to be grownoutside their stated hardiness zones.Other species may be found tohave cold tolerance greater thanreported due to heat island effects orlocal microclimates. ‘‘Heroic’’ efforts,such as portable greenhouses andheating tapes, are also employed togrow palms far outside the normallyaccepted range for a given species,but these efforts are not always

practical nor recommended for typi-cal landscape situations. Otherspecies may prove to have cold toler-ance, but because of lack of seed, poorgermination, slow growth, or otherfactors such as expense, are hard tofind commercially and are usu-ally limited to palm enthusiasts’collections.

The use of palms in landscapedesigns is often grouped according toleaf morphology or growth habit(Arnold, 2008). Typical groupingsby leaf morphology would includefeather palms (pinnate leaves) versusfan palms (palmate or costapalmateleaves). Among the most commonlygrown cold-hardy feather palms read-ily available in the U.S. nursery tradeare jelly palm, mule palm, date palm,and canary island date palm (Tables 1and 2; Fig. 1). Generally speaking, thejelly palm is the most cold tolerant ofthese feather palms (Arnold, 2008).Among the most cold hardy of thecommonly available fan palms are theneedle palm, dwarf palmetto, wind-mill palm, cabbage palm, mediterra-nean fan palm, and texas palmetto(Tables 1 and 2; Fig. 2). Some ofthe most cold-hardy palms, such asneedle palm and the dwarf palmetto,have only short trunks or fronds thatarise at or near ground level (Arnold,2008). These short palms have theirapical meristems (growing points)near the soil, which is presumed tohelp in insulting them from coldtemperatures compared with exposedbuds positioned high above theground in taller palms. However,there is no correlation of trunkheight with hardiness as arborescent

Table 1. Palm species native to the continental United States with associated USDA plant hardiness zone ratingand native range.

Common name Scientific name Zone rating Native range

Everglades palmetto Accoelrrhaphe wrightii 8b FloridaFlorida silver palm Coccothrinax argentata 9b FloridaKeys thatch palm Leucothrinax morrisii 9b FloridaNeedle palm Rhapidophyllum hystrix 6b Alabama, Florida, GeorgiaFlorida royal palm Roystonea regia 9a FloridaScrub palmetto Sabal etonia 7b FloridaTexas palmetto Sabal mexicana 8b TexasDwarf palmetto Sabal minor 7a Alabama, Arkansas, Florida, Georgia, Louisiana,

Mississippi, North Carolina, Oklahoma, Texas,South Carolina

Cabbage palm Sabal palmetto 8a Florida, Georgia, South Carolina, North CarolinaSaw palmetto Serenoa repens 8a Alabama, Florida, Georgia, MississippiFlorida thatch palm Thrinax radiata 9 FloridaCalifornia fan palm Washingtonia filifera 9 Arizona, California

Table 2. Palm species commonly used in cool or temperate landscape plantingsand associated USDA plant hardiness zone ratings.

Common name Scientific name Zone rating

Blue hesper palm Brahea armata 8aJelly palm Butia capitata 8bMule palm · Butyagrus nabonnandii 8bBamboo palm Chamaedorea spp. 8bMediterranean fan palm Chamaerops humilis 8aChilean wine palm Jubaea chilensis 8aMazari palm Nannorrhops ritchiana 8aCanary island date palm Phoenix canariensis 8bDate palm Phoenix dactylifera 8bNeedle palm Rhapidophyllum hystrix 7aTexas palmetto Sabal mexicana 8aDwarf palmetto Sabal minor 7aCabbage palm Sabal palmetto 8aSaw palmetto Serenoa repens 8aQueen palm Syagrus romanzoffiana 9aWindmill palm Trachycarpus fortunei 7bMexican fan palm Washingtonia filifera 8a

Washingtonia robusta 9a

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cold-hardy palms such as the windmillpalm, cabbage palm, or texas pal-metto that can be grown in USDAplant hardiness zones 7 or 8 (Tables 1and 2). There are even cold-hardypalms with multiple trunks, suchas mediterranean fan palm andmazari palm (Nannorrhops ritchiana)(Fig. 3).

Selection of provenances fromcolder portions of marginal speciesranges or little-known species thatmay prove cold hardy are beginningto enter the U.S. landscape trade,such as the kumaon palm (Trachycar-pus takil) from the Himalayan re-gion of India. These genotypes mayoffer even greater diversity of cold-hardy selections in the coming yearsfor landscape designers. There aremany examples of trees grown forforestry purposes where prove-nances from high latitudes or highelevations have been used to extendthe use of species to colder envi-ronments than is typical for the spe-cies (Zobel et al., 1987). Therewould appear to be good potentialfor this strategy to be employed toidentify genotypes of native andexotic species of palms for which theirreliable use could be extended tomore northern locations in U.S.landscapes.

Factors affecting coldtolerance

Many factors can influence coldhardiness in palms (Ingram andYeager, 1982, Ingram et al., 1985).These factors include acclimation,cool down conditioning, and mineralnutritional status. Duration of coldmay be as important as the absoluteminimum temperature exposure indetermining survival. Certain palmspecies may be able to survive lowtemperatures of a short duration.Humidity and precipitation levelscan also have an effect, with manypalms from semiarid regions suc-cumbing to subfreezing temperaturesin the humid, higher rainfall south-eastern United States, while remain-ing unaffected at similar subfreezingtemperatures in semiarid climatessuch as northern and central Texasand eastern Oklahoma (McClendonet al., 2007). The mazari palms(Frankco, 2003) and california fanpalms (Arnold, 2008) are examplesof palms that survive winters betterin drier climates. A site with goodair drainage with the avoidance offrost pockets can mitigate cold tem-peratures. Another factor affectingsurvival is the amount of leaf desic-cation from high winds that occurs

when root uptake of water is mini-mum during cold temperatures.

Mitigating cold damageto palms

Proper species selection is thebest way to ensure survival of palmsin colder climates, and the correctspecies may vary with regions thathave the same USDA plant hardinesszone rating (Arnold, 2008). Of sim-ilar importance is the selection of thecorrect site and microclimate in thelandscape, which can affect palm sur-vival in marginal areas (Francko,2000). Placing plants on the southside of a wall or in courtyards can trapradiant heat from the sun and there-fore reduce the amount of time a palmis exposed to subfreezing tempera-tures. Walls, evergreen hedges, oroverhead tree canopies can providewindbreaks to minimize wind expo-sure and reduce leaf desiccation dam-age. Avoid planting palms in low areaswhere poor air drainage may formfrost pockets.

Active winter protection techni-ques can include simple shelters, windbarriers, natural insulation materials,trunk and/or foliar wrapping, tem-porary greenhouses, and various heat-ing devices (Frankco, 2003). Simpleshelters include placing a blanket orplastic bubble sheeting over the palm.Wind barriers, such as burlap or land-scape fabric supported around a palmcan reduce desiccating winds. Windbarriers or simple shelters can beaugmented by placing loose mulchor other loose insulating materialsaround the palm. When such a tech-nique is used, some sources cite spray-ing the stem and bud with a broadspectrum fungicide and/or bacteri-cide to reduce chances of bud rot(Frankco, 2003). Layering accumu-lated pruned dead palm leaves in anoverlapping thatched-roof or ‘‘tikihut’’ pattern can help to divert rainfalland snow or ice melt from collectingin crevices in the bud and immaturespear leaves where repeated freezingand thawing may damage tissues lead-ing to crown rots.

More elaborate cold protectionmethods such as trunk and foliarwrapping or heating trunks or eventhe whole plant using a temporarygreenhouse can be effective for im-portant specimen palms, but will re-quire much more effort and expense

Fig. 1. Commonly grown cold-hardy feather palms readily available in the U.S.nursery trade are jelly palm (A), date palm (B), and canary island date palm (C).Images copyrighted by M.A. Arnold.

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(Frankco, 2003). It is critical to pro-tect the trunk and apical meristempoint, as most palms species have asingle growing point per trunk. Oncethis growing point is damaged orkilled, palms do not typically producethe adventitious buds that allow manydicotyledonous trees and shrubs torecover from severe cold damage(Arnold, 2008). Trunks and growingpoints can be wrapped with a varietyof insulating materials (Fig. 4, A–C).Palm leaves are often tied up in a tightbunch around and above the growingpoint to help insulate the apical mer-istem and to prevent desiccation ofthe leaves (Fig. 4C). Heating pads,heat tape or pipe wraps, low wattageheat cables, or strings of lights can beused for high value or prominentspecimens. Frankco and Wilhoite(2002) report that strings of C9 lightsalone wrapped around palms can add1 to 2 �C to the ambient air temper-ature and that using them underinsulating wrap increases the temper-atures 6 to 9 �C.

Of course, temporary green-houses ranging from plastic coverswith a light bulb to more elaborateportable glass or plastic structurescan be highly effective in shelteringpalms during cold temperatures. Oneadvantage of such structures is thatthey may also provide some heat tothe root zone (Frankco, 2003).Avoiding frozen soils will help toensure moisture flow to the leaves,reducing the chances for desiccationdamage.

Future opportunities for incor-poration of palms in cooler climatelandscapes appear favorable as newintroductions, from underused spe-cies to more cold-hardy provenanceselections from more commonlygrown species, are introduced to thetrade. Various maintenance practicescan be implemented to expand thesedesign possibilities even further.Nearly all palms can be successfullyestablished in at least one cold hardi-ness zone lower (colder) throughsecuring a microclimate and utiliza-tion of other techniques describedabove. Cold-hardy palms add aunique character to landscapes thancannot be duplicated with otherspecies, resulting in a greatly ex-panded plant palette for landscapedesigners and architects, and creatinga new niche market for the nurseryindustry.

Fig. 2. Commonly grown cold-hardy fan palms are the needle palm (A), windmillpalm (B), mediterranean fan palm (C), dwarf palmetto (D), cabbage palm (E),and texas palmetto (F). Images copyrighted by M.A. Arnold.

Fig. 3. Cold-hardy palms with multiple trunks, such as mediterranean fan palm (A)and mazari palm (B). Images copywrited by M.A. Arnold.

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Literature citedArnold, M.A. 2008. Landscape plants forTexas and environs, 3rd ed. Stipes Pub-lishing, Champaign, IL.

Black, R.J. 2003. Native Florida plants forhome landscapes. Inst. Food Agr. Sci.,Univ. Florida, Dept. Environ. Hort. FactSheet ENH-25.

Englehart, P.J. and A.V. Douglas. 2003.Urbanization and seasonal temperaturetrends: Observational evidence from adata-sparse part of North America. Int.J. Climatol. 23(10):1253–1263.

Francko, D.A. 2000. Effect of microcli-mate variation on cultivation of cold-

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Frankco, D.A. 2003. Palms won’t growhere and other myths: Warm-climateplants for cooler areas. Timber Press,Portland, OR.

Frankco, D.A. and S. Wilhoite. 2002.Cold-hardy palms in southwestern Ohio:Winter damage, mortality, and recovery.Palms 46(1):5–13.

Ingram, D.L. and T.H. Yeager. 1982.Cold protection of ornamental plants.Inst. Food Agr. Sci., Univ. Florida, Dept.Ornamental Hort. Fact Sheet OH-1.

Ingram, D.L., T.H. Yeager, and R.L.Hummel. 1985. Cold protection fornursery crops. Inst. Food Agr. Sci., Univ.Florida, Bul. 201.

Little, E.L., Jr. 1977. Atlas of UnitedStates trees. Vol. 4. Minor eastern hard-woods. U.S. Dept. Agr. Misc. Publ. 1342.

McClendon, T., W. Roberds, and J. LeVert.2007. Hardy palms for the Southeast.Southeastern Palm Soc., Apison, TN.

Oke, T.R. 1987. Boundary layer climates.Routledge, London.

Oke, T.R. 1997. Urban climates andglobal environmental change, p. 273–287. In: R.D. Thompson and A. Perry(eds.). Applied climatology: Principlesand practices. Routledge, London.

Riffle, R.L. 1998. The tropical look: Anencyclopedia of dramatic landscapeplants. Timber Press, Portland, OR.

Riffle, R.L. and P. Craft. 2003. An ency-clopedia of cultivated palms. TimberPress, Portland, OR.

U.S. Department of Agriculture. 1990.USDA plant hardiness zone map. U.S.Dept. Agr. Misc. Publ. No. 1475.

Vines, R.A. 1960. Trees, shrubs, andwoody vines of the Southwest. Univ.Texas Press, Austin, TX.

Zobel, B.J., G. van Wyr, and P. Stahl.1987. Growing exotic forests. Wiley, NewYork.

Fig. 4. Mexican fan palm trunks (A) and apical meristems (B) can be wrapped witha variety of insulating materials. Tying the leaves up around the apical meristem(C) can also be used to help protect the growing point and minimize desiccationdamage. Images courtesy of H.B. Pemberton.

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