PALMS Francko : Co ld -ha rdy pa lms Vo lume 44 (1 ) 2000

Effect ofMicroclimateVariation onCultivation ofCold-Hardy Palms inSouthwestern OhioAlthough the great maiority of palms are tropical to subtropical in distribution,

several cold-hardy genera are being grown successfully in warm-temperate gardens

world-wide (reviewed by Gibbons & Spanner '1.999). The term 'cold-hardy palm' is

subiective and can be used to describe plants that survive brief exposure to light frost

to those that are leaf-hardy in sub-zero (Fahrenheit) temperatures (Riffle 1998). In this

paper, I focus on cold-hardy palms that have been reported to survive approximately

-1,5 to -29"C (ca. 5 above zero to -20"F) temperatures.

Not surprisingly, most of the literature dealingwith cold-hardy palm horticulture in NorthAmerica focuses on plants grown in USDA Zone7b and south (reviewed in SPEPS 1994, Riffle1.998), and even in Zone 7b palms are stillconsidered somewhat of a novelty by mostlandscapers and the gardening public.Nonetheless, the references above, numerousInternet websites, newsletter publications (e.g.,Rhapidophyllum) andpublished reports from a fewindividual growers (e.g., pioneering work of Myers1985) provide evidence that several palm speciesmay be grown in Zone 7 and even farther north,provided that attention is given to site selection,proper cultural practices and some winterDrotection.

Despite these insights, there remains a dearth ofprimary literature that critically evaluates thesuccess of cold-hardy palms, in the context ofmicroclimatic variations. in USDA Zones 6a

through 7a. Here I report data on first-yearsurvivorship and vegetative growth of several cold-hardy palm species and varieties at the Hardy PalmDemonstration Plot of Miami University, OxfordOhio (USA), and replicated plots at my somewhatcolder home garden a few km southwest, withspecific relationship to winter seasonmicroclimatic variation at each site.

Matetials and Methods

Study Sites. The Miami University Main Campusin Oxford is located in Butler County,southwestern Ohio (39' 30' N, 84' 42' W)approximately 50 km northwest of Cincinnati and35 km north of the Ohio River. This area liesprimarily in USDA Plant Hardiness Zone 6a,although urban areas and the immediate OhioRiver valley are classified Zone 6b (USDA 1990).The growing season in Butler County ranges fromapproximately 180-195 days depending on

Devro A. FnaNcxoDepartment of BotanyMiami UniversityOxford, Ohio 45056 USA

PALMS 44(1):3746 3 7

PATMS Francko : Co ld -ha rdy pa lms Volume 44(1) 2000

Alcove

Crepe Myrtle'Acoma' OCrepe Myrtle 'Tonto'

O

Southern Magnolia 'Edith Bogue'

1 . Summer 1998 plant location grid for the Alcove and Wall subplots at the Hardy Palm Demonstration Plot (HPDP,located on the SE corner of Pearson Hall, Miami University.

'l = Rhopidophyllum, 4-year old seedling; 1 a =Rhapidophyllum, ca. 7-8-years old; 2 = Sobal minor, 2-3-year old seedling; 2a = Sobol minor, 6-7-years old; 3 = Sobalpolmetto, 2-year old seedling; 4 = Sobal sp. Brazoria palmetto, 2-years old; 5 = Trochycarpus fortunei, 2-3-years old; 5a =Trachycarpus fortunei, 6-7-years old.

microclimate. The mean annual temperature islpproximately I2.2"C (54'F), with typically hot,dry summers and cool to cold winters. Totalannual precipitation and snowfall average about195 cm and 43 cm, respectively. From a phyto-geographic perspective southwestern Ohio,northern Kentucky and southeastern Indianarepresent a vegetational ecotone representative ofboth northern and southern U.S. flora, includingstands of beech-maple forest and mixedmesophytic forest interspersed with row crop

agriculture and a prairie remnants (Vankat1979).

5a

The Hardy Palm Demonstration Plot (HPDP) wassited on the SE corner of Pearson Hall, a four-storybrick building that houses the biological sciencesdepartments it Miami. The site includes a 15 mZalcove plot and a rectangular plot (ca. 1 x 10 m)immediately adjacent to a 2.5-m high brick wall(Fig. 1). The building itself and wall extendingsouth from it largely block the cold west andnorthwest winds of winter storms. I hypothesized,

Wall

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PALMS Francko : Co ld -ha rdy pa lms Vo lume 44 (1 ) 2000

1. Winter minimum temperatures at rural Western Knolls site, Oxford, Ohio, yea1989 through 1999

1989-90 90-97 9r-92 92-93 93-94 94-9s 9s-96 96-97 97-98 98-99-28.9 -21.. t -18.9 -77.7 -18.9 -31.1 -25.5 -18.3 -13.9 -25.5

-20 -6 -2 0 -2 -24 -I4 -1 7 -14

OC

"F

based on some limited winter minimumtemperature measurements collected in previousyears, that these campus plots would effectivelyrepresent Zone 6b-7 a microhabitats.

A second set of plots was established at my homegarden in the Western Ituolls (WK) area of Oxford,located ca. 5 km southwest of Pearson Hall in arural area at the edge of the city limits. Winterminimum temperature data I had collected duringthe past nine years in this neighborhood suggestedthat the low-lying forested part of the propertyon the west and north sides of our home likelyrepresented a Zone 6a microhabitat, while areasnear the house on the south and east side werelikely Zone 6b.

Site Preparation and Palms Utilized. In conjunctionwith the Miami University Campus Services Office,

the HPDP sites were tilled in July 1998 and thehealy clay soil was amended with equal parts ofleaf compost, topsoil and sand to a depth of about15-18 cm, resulting in a well-drained soil ofslightly acidic pH. At the WK plots, soils awayfrom the house are well-drained, fertile forest loam(pH ca. 6.8) and were not amended with organicmatter or sand, but planting beds near the housewere amended with compost, sand and humus.

In this pilot proiect, palms were obtained fromseveral sources. Smaller, 2 to 3-yearold, bare-rootseedlings of Rhapidophyllum hystrix (needle palm;N = 7), Sabal minor (dwarf palmetto; N = 6),Trachycarpus fortunei (Chinese windmill palm;Charlotte variett N = 7), Sabal sp. (Brazofiapalmetto; N = 3), and Sabal palmetto (cabbage

2. Appearcnce of the HPDP in August 1998 showing general site and smaller palms. The larger dwarfpalmetto and needle palms had not yet been installed.

r-EllE

ffi

3 9

PALMS Francko : Co ld -ha rdy pa lms Vo lume 44 (1 ) 2000

2. \ /inter minimum temperatures and mean low temperatures at various sites on the Miami

University campus and at the Western Knolls (WK) site for the 9 coldest nights from December 1to March 1999. Mean values computed for three temperature recording stations each at WK Forest/NeaHouse and Uoham courtvard, and two stations each for Pearson Wall, Irvin. Cincinnati and Hamil

per National Weather Service data reported in the Cincinnati Enquirer for the same datesampus/WK data

WK Pearson Uoham Irvin Hiestand Cincinnati Hamilton

Forest/Near House Control/Alcove/Walloc -25.51-23.9 -22.81-19.41-1,9.4 -19.4 -18.9 -\9.4 -22.2 -22.2

MinoF -r4l-tL -91-31-s -3 -2 -3 -8

-27.2

6.r

-8

c n A

8 .4

oc -77.31-2L.7 -21.41-23.31-23.2

Mean

-23.5 -23.8 -23.4

oF 3.u7.O 6.6le.ele.8 10.3 10.8 10.1

palm; N = 4) were obtained via mail order fromPlant Delights Nursery, NC. Larger specimens ofneedle palm (6-7 years old; N = 4) and Chinesewindmill palm (10 gallon size; N = 2) wereobtained via mail order from Forest Sound Nurseryin NC. In addition to these demonstrably cold-hardy species, I included a Livistona chinensis

(Chinese fan palm) purchased from a localdiscount store. Also included in the WK plotanalysis was a small specimen of Trachycarpus

fortunei, originally purchased in Georgia in March1995 and moved to its current location at mypresent home (west side of house next to a smallornamental pond and ca. 1.5 m from the

3. One of the large needle palms and S. minor during mid-Jantary 1999 showing maximal extent of snow drifts.

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PALMS Francko : Co ld -ha rdv oa lms V o l u m e 4 4 ( 1 ) 2 O O 0

foundation) in October 1997. This plant hadreceived winter protection from a plastic shelterbut had been grown outside continually.

Although it is advisable to plant palms early in thegrowing season, especially in marginal climates(SPEPS 1994), plant availability and other logisticsprevented us from getting plants in the grounduntil early-late August 1998. At the HPDP site (Fig.1) bare-root plants were planted directly into soiland were mulched with pine straw. Larger palmswere carefully removed from pots prior to plantingand mulched as above. At the WK site, one largerneedle palm was planted near the front of thehouse (SE exposure) roughly 3 m from thefoundation. A 10-gal Tiachycarpus was also plantedon the front side near the SE corner of the homeand next to the foundation. The Livistona wasplanted on the SE side of my home next to a porchand next to the foundation. At the edge of theZone 6a forested area at the back of my propertyI planted one each of the small Trachycarpus andneedle palm specimens. All palms were fertilizedin late summer with a slow-release granularfertilizer containing micronutrients.

In December 1998, a burlap wind barrier (75 cmheight) was placed around plants at the both theHPDP and WK sites. Each plant was treated withantidessicant spray (Wilt-Pruf) and root zones weremulched to a depth of ca. 8 to 10 cm with pinestraw. The Livistona specimen at WK was enclosedwithin a plastic lean-to. Since most plants werevery small and were planted late in the growingseasonr and since I had no way of knowing howcold it might get in the plots, I elected the optionof being able to provide a small amount ofsupplemental heating to protect spear leaves andbud tissue during the coldest weather. I ran 15 ft(4.6 m),30-watt heat cables through the plots sothat the cable was adjacent to the growing spearof each plant. In Iarger Trachycarpus and Sabalspecimens and in the Livistona enclosure, the cablewas draped loosely around the base of the plant.Since the cables used generated ca. 2 watts of heatper foot (0.067 watts/cm), the amount ofsupplemental heating ranged from < 1 watt insmaller plants to perhaps 15 watts in the largerclump palms. Although the heat cables wereequipped with thermostats that activated atapproximately 2.7'C (38'F), they were plugged inonly when nighttime lows were forecast to bebelow -12.2"C (10'F). The bare-root needle palmand Trachycarpus were grown in the cold forestsite at WK without supplemental heat.

Temperature Measuremenfs. Winter temperaturedata were collected within the HPDP and WK plotsin order to provide definitive microclimatic

parameters for the first-year experimental plots.Simple thermometers with inside-outside probeswere placed on wooden dowel rods approximately20 cm above the ground. Each thermometer wascalibrated prior to use with a YSI thermistortemperature meter and field temperature readingswere corrected accordingly. Two thermometerswere sited in the wall plot at the HPDR one ca. 5m from the building and the other at the distal endof the plot. Another temperature station wasIocated in the alcove at the HPDP.

Although 1998 palm plantings on campus wereconfined to the HPDP, my intent was to introducenew experiemental palm pots on the MiamiUniversity campus in 1999. To evaluatemicroclimatic variation on campus and propertlysite these plots, additional measurement sites wereestablished on campus in two groups of settings:1) sheltered areas where large buildings blockedthe north and west winds (Upham Hall, Irvin Hall,and Hiestand Hall courtyards) and Z) an open arcacontrol exposed to normal winter wind patterns(w. side of Pearson Hall).

At the WK site, temperatures were recorded inpalm plots near the house and at the forest controlsite. Temperature measurements were recorded tothe nearest Fahrenheit degree within 30 min priorto dawn, at the coldest period of the overnighthours, both outside and inside burlap enclosures.Since the Miami campus does not have an officialweather reporting station, I also collectedpublished temperature data for the officialreporting stations at both the Greater Cincinnati-Northern Kentucky International airport (theofficial National Weather Service site forCincinnati, ca. 45 km south of Oxford in Hebron,KY) and the Hamilton-Fairfield Airport (ca. 25 kmsoutheast of Oxford). Both of these sites lie at theinterface of USDA Zones 6a and 6b, but becausesuch larger-scale climatic maps do not reflect theheat-island effect of large airports, these sitesalmost certainly reflect mid-Zone 6b conditions.

Results and Discussion

Microclimate Determinations. As noted earlier, I havecollected winter temperature minima data for therural Oxford habitat in WK since the winter of1989-90. Thus, with data from the winter of1998-99 I had a ten-year minimum temperaturedata set which could be used to place 1998-99data in historical context. On the basis of winterminimum, 7998-99 proved to be the third coldestin the past decade (tied with 1.995-96), with a lowof -25.5"C (-14'F) recorded in the predawn of 5 Jan1,999 at the WK forest site (Table 1). The ten-yearmean winter minimum of -7.5'F (-22'C\ that Irecorded for the rural WK area, awav from houses

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PALMS Francko : Co ld -ha rdy pa lms V o l u m e 4 4 ( 1 ) 2 O 0 O

and other structures, lies in the mid-range of USDAZone 6a (-5 to -10'F), in agreement with Oxford'sZone 6a classification in USDA Zone maps of theUnited States. Howeveq Table 1 also suggests thatsimple mean winter minimum data do not tell acomplete story. Rather, the ten-year data set wasmarkedly bimodal. Only a single year (1990-91)featured a minimum temperature within the Zone6a range; five years were warmer (including theEl Niflo winter of 1997-98) and four were colder(including the winter of 1994-95, which tied theall-time record low for Oxford of -31.1'C (-24"F).Furthermore, the duration of cold spells, animportant variable in plant viability, is not obvioussimply from winter minima data. In 7998-99, fotexample, I recorded nine nights where thetemperature at the coldest recording station (theforest at WK) dipped below -9.5"C (15'F); nonights save 5 Jan 1999 were below zero Fahrenheit,and only four nights reached lows of -17.8'to -

15'C (0 to 5'above zero F). Over the past tenyears, I can reliably estimate than no more thaneight to ten nights have dropped to -23.3"C (-10'F)or below at WK. Put another way, if a given plantis killed by temperatures below -23"C, it wouldhave been at risk only eight to ten days out ofmore than 3600.

Winter minimum temperatures and the mean lowtemperature for the nine coldest nights in1998-99varied greatly between sites, suggesting that themicroclimate on the Oxford campus sites and atWK sites with respect to minimum temperature atthe Miami campus sites and at WK sites varied atleast a full USDA zone (Table 2). In the HPDP, thewinter minimum outside the burlap barriers was-L9.4'C (3'F) at both recording stations along thewall and in the alcove. Although the heat cableswere activated on the coldest nights, thetemperature within the barriers was generally thesame or at most 1-2"F warmer. Since nightly heatradiation from the wall and the buildingundoubtedly contributed some heat, I concludethat the heat cables were likely ineffective at theHPDP site, although I could not rule out a smallheat differential immediatelv adiacent to thecables.

Winter minima and the mean low for the coldestnine nights at the other protected campus sites(Upham, Irvin, Hiestand) were similar to those atthe HPDP ffable2\. Winter minima and the meanwinter low temperatures at the exposed controlsite on campus (-22.8"C; -9'F), sites near our housein WK (-23.9"C; -11'F) and the official NWS sitesin Cincinnati and Hamilton (-22.2"C; -8'F) weresimilar to each other and consistently a fewdegrees F colder than the warmest sites on campusrTable 2).

Based on a comparison with the ten-year data setfor the cold forest temperatures at WK (meanwinter minimum = -21.9"c (- 7.5 "F), the winterminimum in 1998-99 of -25.5'C ( -14"F)

represented a departure of -3.6'C (-6.5'F) fromnormal. The official 1998-99 winter minimumreadings from Cincinnati and Hamilton of -22.2"C(-8'F) were similarly on the order of 4-6 degrees Flower than the mid-Zone 6b rating for these sites.Hence, my data suggest that the protected sites onthe Miami campusr which reached -18.9 to -19.4'C(2 to -3'F) minima, might be expected to drop toca. -76.7 to -15.5 'C (3-4 above zero 'F) in astatistically normal winter, and thus represent mid-USDA Zone 7a microhabitats. By the samereasoning the exposed areas of campus and areasimmediately adjacent to houses at WK areprobably best considered Zone 6b microhabitats,and rural Oxford away from structures is clearlyZone 6a.

Survivorship and Condition of Palms. Photographsof palms during summer 1998, winter 1.998-99,and spring 1,999 at the HPDP and at WK are shownin Figs. 2 to 7 , respectively. All of the small seedlingpalms, whether grown at the HPDP or at WK sites,survived the winter of 1998-99 and were growingwell by mid-sping7999 (Figs. 4, 5 and 7). Damageto small seedling palms was confined to leaf tipburn on all plants and margin burn on mostplants. No spear leaves were lost in smallTrachycarpus, Rhapidophyllum, S. minor, Sabal sp.(Brazoria) or S. palmetto seedlings at either plot. Bythe end of the 1999 growing season (mid-Nov),seedling palms of all species had approximatelydoubled in height, Ieaf number and trunkdiameter.

Similarly, the large Sabal minor and three large R.hystrix installed at the HPDP suffered tip andmargin burn, especially to leaves that werecompletely exposed to drying winds (Fig. 4). Of atotal of 16 needle palm trunks among the threelarge plants, five trunks partially defoliated andlost their spear leaves. Despite immediatetreatment with fungicide (Myers 1999), only twoof the five trunks regenerated new spears by theend of the 1,999 growing season (mid-Nov),although each of the large needle palms developedseveral new lateral trunks. Each of the other 11undamaged trunks grew at least two expandedleaves and a spear leafin1999.

One of the large Trachycarpus specimens plantedin the HPDP alcove succumbed in mid-fall 1998to an unknown malady. Despite care in plantingand adequate water, leaves began to yellow andsenesce on this plant almost immediately.

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PALMS Francko : Co ld -ha rdy pa lms Vo lume 44 (1 ) 2000

Although it was treated with fungicide and apyrethrin-based insecticide, it was defoliated, andlive bud tissue was absent before winter began.Similarly, the second large Trachycarpus, whichwas planted on the SE side of our home at theWK site, began to senesce soon after planting. Itdid appear to recover somewhat, and entering thewinter season still had six to eight reasonablygreen and healthyJooking leaves. Late fall 1998was extremely mild, with some high temperaturesreaching the 23'C ( mid-70s "F) in early December.However, late December brought the first real coldof the season, with72 hours of continuous belowfreezing temperatures and nighttime lows in thehigh single digits F. At the end of this cold snap,this palm was approximately one-half defoliated,and became completely defoliated after exposureto -17.8'C (0'F) outside the enclosure; the insideprobe was covered with light snow and reachedonly -14.4'C (6'F) on lJanL999. Despite tungicidetreatment the spear could be pulled loose by theend of February and no live bud tissue remainedin cut cross sections of the trunk in March 1999.

At the WK plots, the large needle palm planted onthe southeast side of the house suffered leafiniuries similar to but no worse than the largerneedle palm specimens at the HPDP and only oneof five trunks lost its spear (Fig. 7). This wassomewhat surprising, since the minimumtemperature I recorded within burlap enclosuresurrounding the WK needle palm reached -24.4"C

(-L2'F) on the morning of 5 Jan 1999, ot ca. 5'C(9'D colder than the minimum at the same timein the HPDP plot (Fig. 6). By mid-May, this planthad several expanded new leaves and new spearsgrowing in. The Trachycarpus specimen growingnear the ornamental pond on the west side of ourhouse appeared undamaged prior to 5 Jan 1999,but most of the leaf tissue above the middle ofeach petiole was killed by a temperature thatdropped to ca. -23"C (between -9'and -10'F) in theleaf crown that predar,vn. Although the bases of thepetioles remained green, the terminal spearultimately came loose from this palm by latewinter. Liquid fungicide was poured down intothe crown approximately monthly beginning in

January (Myers 1.999), and by mid-May t999, thepalm had begun to recover, with two new spearleaves apparent. By November L999, this planthad five fully expanded leaves and an expandingspear leaf.

The needle palm and Trachycarpus seedlingsplanted in the Zone 6a forest area of WK bothsurvived the winter. Although the latter wasdefoliated, its spear never pulled loose and it nowhas one new expanded leaf and a second

expanding spear. Except for some minor leafspotting, the needle palm was undamaged byexposure to the -25.5"C (-14"F) minimum at thissite. Foliar growth will be slower at this site dueto the deciduous tree canopy and part shade lightregime.

Amazingly, the Livistonq chinensis specimenplanted near our house and covered with a plasticlean-to survived the winter. The temperature insidethe enclosure dropped to a low of -10.5'C (13"F)on the morning of 5 Jan L999, approximately11.1,-72.2"C (20-22"F) above that outside theenclosure due to heat from the house and the heatcable wrapped around the plant base and a layerof insulating snow on the top of the enclosure. Atthis temperature, defoliation was complete. I hadnoted severe scorching of most leaves on thisspecimen when temperatures inside the enclosurefirst dropped below about -3.9'C (25'F) in lateDecember. Despite complete defoliation, new speargrowth commenced in mid-May from all fivetrunks of this plant and by late-June 1'999, itpossessed five small fan leaves ca. 15-2O cm across.These leaves continued to enlarge during 1999,and by mid-November the plant was ca. 50-60cm tall and a meter across. My data suggest thatLivistona chinensis may be a 'deciduous' palm inZone 6, capable of regenerating new foliage in thespring as long as bud tissue is not destroyed bycold.

Additional Considerations: Some additionalconsiderations are necessary in order to fully assessthe data. In addition to minimum temperature,several environmental factors can affect winteriniury in broad-leaved evergreens. The wind chillfactor dictates how rapidly leaves lose water andare therefore sublect to dessication andwinterburn. The presence of snow or ice coverreduces wind-induced dessication and alsoinsulates the ground and plant tissues from coldexposure.

As noted earlier, the winter of 1'998-99 was a verymild until the last week in December and the firstmeasurable snowfall (ca. 1 cm) occurred on 30Dec 1998. Although the air temperature neverdropped below the high single digits above zeroF even in the coldest areas and the high teens inwarmer areas, the recorded wind chilltemperatures were ca. -18 to -20'C (0 to-S"F, datafrom the Hamilton-Fairfield Airport). Thefollowing night an additional 6-7 cm of snow fell,and on Z Jan'1,999 this was supplemented by18-20 cm of fresh powder. Both the amount ofsnow and the direction of the storm winds (fromthe east and southeast, gusting above 20 mph)were unusual for this area, and the HPDP and WK

44

PALMS Francko : Co ld -ha rdy pa lms Vo lume 44 (1 ) 2000

.1. '.: t ' . .it$:l'/rt

@j

6. Needle palm on the front side of the house at the WKplot in mid-lan 1999, showlng snow dri f ts around theenclosure.

7. The same palm as in Fig. 6, ful ly recovered andactively growing plant, luly 1999, with newly instal ledSobal oalmetto in backoround.

plots on the southeastern side of our home, whichare protected from prevail ing north and westwinds of winter, were hit by the brunt of thestorm. Windchill readings reached -23 to -26"C(-10 to -15'F) for long periods of t ime (gustsproduced -35'C [-30'F] windchil ls) and snowdrifted heavily over the burlap barriers and on topof plants (Figs. 3, 6), covering all but the upperone-half of the larger palms. Continued cold andadditional snow plus an ice storm on 8-10 Jan1999 produced the longest continuous snow/icecover duration (nearly three weeks) recorded inOxford since the winter of L977-78. Based on theinability of my burlap barriers to prevent snowdrifting inside the enclosures and theaforementioned observation that temperaturesinside the burlap enclosures were nearly identicalto those outside, I conclude that simple burlapbarriers probably represented an ineffective winterprotection strategy under these conditions.

The long-term snow/ice cover had two effects ofimportance for palm damage and recovery. First,the fact that most plants were completely coveredby snow and ice for nearly three weeksundoubtedly contributed to some of the leafdamage noted on all plants. Howeveq plant tissues

covered by snow and ice were also insulated fromthe worst of the cold to a remarkable degree. Onthe coldest morning of the winter (5 Jan 1999) Itook temperature measurements approximately8-10 cm below the surface of the snow in theforest plot area of WK. The readings of -9.4 to -8.9'C (15-16'F) were fully 77"C (30'F) warmerthan the air temperature above the snow. Similarly,temperature readings under the snow inside thesnow-covered burlap enclosures at the HPDP neverwent below -5'C (23'F), again some

'J.4"C (25"F)above ambient. Windchill factors were bydefinition not operative in plants sheltered by acovering of snow and ice. Thus, although the tipsof larger plants at the HPDP and approximatelythe upper one-half of the foliage of larger palmsat the WK site were exposed to extremely lowwind chill temperatures as well as below zero Fambient temperatures, entire smaller plants andthe basal portions of larger plants were not thusexposed.

The dual effect of snow and ice cover hasimportant ramifications to potential palm growersin the Upper South or Lower Midwest. In theseparts of the United States, snow cover is sporadicin most years, and extremely cold temperatures

45

PALMS Francko : Co ld -ha rdy pa lms Vo lume 44 (1 ) 2000

(i.e., below -17'C or 0'F) almost never occur unlessthe relatively warm ground is covered by snow orice, which promotes high radiational cooling andrapid temperature drops after sundown. The factthat none of my snow-covered small palms waskilled, even the S. palmetto seedlings, suggests thatthe same meteorological conditions that fosterextreme, potentially killing cold also can alsoinsulate small plants from those conditions.

In summary, I report a high degree of success infirst-year survivorship and subsequent growth ofall palm species and varieties examined, evenunder winter conditions that were more rigorousthan typical in SW Ohio. Moreover, the effectivemicroclimate to which plants were exposed rangedover a full USDA zone (6a to 7a), suggesting thatthe hardiest of the cold-hardy palms, includingRhapidophyllumhystrix, S. minor and perhaps someof the hardier Trachycarpu.s varieties should be ableto be grown with little or no winter protection inSW Ohio, so long as attention is given tomicroclimate.

Future Directions: Based on 1998-99 trials and thetemperature profiles for campus and WKmicrohabitats, we have expanded the scope of thepalm cultivation trials to include more varieties,a larger range of plant sizes, and several newexperimental plots (Fig. 2F). A total of ca. 70 palmswere planted on the Miami-Oxford campus, at theWK site, and at Miami's Middletown campus (ca.30 km E. of Oxford) during April-early June of1999. Most of the new plants were obtained fromNeotropic Nursery in Georgia in person (i.e., notmail order), arrd included not only morerepresentatives of species/varieties already undercultivation, but also large (i.e., 10-gal. size)specimens of Sabal palmetto, S. bermudana, S. minor,Serenoa repens and larger specimens of. Tiachycarpus

fortunei. I was also fortunate to obtain fromNeotropic Nursery several fairly large (3-gal)specimens of Trachycarpus takil and WashingtoniafiIifera. In addition, we obtained via mail order,bare-root seedlings of Trachycarpus fortunei (PlantDelights' varieties "Norfolk" and "Greensboro")

and Butia capitata in late winter 1999. These wereimmediately potted into one-gallon peat pots andplaced in the Botany department greenhouse inorder to recover from root shock for 3-4 monthsbefore being planted outside.

In addition, I am employing a modified pot-planting technique in aIl1999 plantings to reduceroot shock set-back and early mortality in largerpalms, as well as to encourage downward rootgrowth during the first critical growing season(Tollefson 1,999). I am slitting the sides ofcontainers 5 cm from the top and carefully slitting

and expanding the lower drain holes on the sideand bottom of the containers prior to placing thepot in the ground. I can only report at this stagethat I have noted no setback in pot-planted palms,and that vigor and growth in the first few monthsafter planting (especially in the larger Trachycarpusspecimens) are far superior to what I noted in lastyear's experimental plantings. Further data will ofcourse be reported as I analyze new and 2-yearo1d plots after the winter of I999-2OO0 andsubsequent spring/summer recovery.

Acknowledgments

This work was supported by the Department ofBotany and the Campus Services Office of MiamiUniversity. I thank Gerry McKiness and TamarMyers for many fruitful discussions and ideas, andmembers of the SPEPS and the IPS who helpedanswer my queries through their respectiveBulletin Boards and member Web pages.

Ltrunarunn CIrul

GrnnoNs, M. aNp T. W. Spauxpp.. 1999. Palms intemperate climates. Palms 43: 91'-93.

Mvnns, T. 1985. Going palmy in Ohio. Principes29:1.24-128.

Myrns T. 7999. Ramblings from the hill.Rhapidophyllum 6(4): 9-11.

Rrrlu,, R. E. 1998. The Tropical Look. AnEncyclopedia of Dramatic Landscape Plants.Timber Press, Portland, Oregon, USA, 428 pp.

SouruEasrERN Parv aNp Exorrc PraNr Socrl,rv.1994.The Palm Reader. A Manual for Growing PalmsOutdoors in the Southeast. www:ces.uga.edu/Agriculture/horticulture/Palmreader. html.

ToLrErsoN, D. 1999. Pot planting: revelations andachievements as the saga continues.Rhapidophyllum 6(3): 8-11.

UNrrpo Srarls DEpanrMENr oF Acnrcurrur.E. 1990.USDA Hardiness Zone Map. AgriculturalResearch Service Publication 1'475, U.S.Government Printing Office, Washington, DC.USA.

VaNxer, J. L. t979. The Natural Vegetation of NorthAmerica: An Introduction.John Wiley and Sons,New York, New York, USA, 261 pp.

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