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Transplanting [W.D. Young & Sons (Indio, Calif.) Time of year to transplant and Ellis Farms (Borrego Springs, Ca- and seasonality of palm root Specimen Palms: lif.); unpublished]. They are typically dug and removed from one landscape growth A Review of site or a nursery fi eld, transported by The most common recommen- truck, and replanted at another site to dation and SIP is to transplant palms Common Practices create an instant mature landscape. during the warmer times of the year, Specimen palms are easy to trans- ideally in late spring or early summer, and Research-based plant compared to large, broad-leaved, because a long growing season is dicotyledonous and coniferous trees, available for regeneration of the root Information which are characterized by large, system (Donselman, 1991; Hodel, multi-branched, woody root systems. 1995, 1996, 1997; Meerow, 1997). 1 A relatively small root ball is neces- However, the landscape industries Dennis R. Pittenger , sary when transplanting most palms of southern California and other Donald R. Hodel2, and because, as arborescent monocots, areas of the southwestern U.S. have they have an adventitious root system been transplanting hardy palms, like A. James Downer3 composed of numerous, simple, fi brous mediterranean fan palm (Chamaerops primary roots that arise independently humilis), canary island date palm (Phoe- and periodically from the root initia- nix canariensis), date palm (Phoenix ADDITIONAL INDEX WORDS. root growth, transpiration, leaf removal tion zone (RIZ) (Fig. 1) at the base dactylifera), queen palm (Syagrus of the trunk (Tomlinson, 1990). It is romanzoffi ana), windmill palm (Tra- SUMMARY. Successful reestablishment standard industry practice (SIP) for a chycarpus fortunei), california fan palm of transplanted palms [members of root ball to extend ≤18 inches (≤45.7 (Washingtonia fi lifera), and mexican the Arecaceae (Palmae)] depends on cm) in radius from the trunk for trans- fan palm (Washingtonia robusta), year- rapid regeneration of roots, avoid- round with variable success to keep ing injury and desiccation of the trees planted palms up to 65 ft (19.8 m) tall during transit and handling, and with trunks 12 to 40 inches (30.5 to pace with year-round demand from maintaining suffi cient soil moisture 101.6 cm) in diameter. Although easy urban development. around the root balls after trans- to transplant, many large specimen Broschat (1998) in Florida report- planting. Since landscape contractors palms do not survive transplanting or ed that palm root and shoot growth and nurserymen spend considerable they require an inordinate length of occurred throughout the year, but were resources and labor transplanting time to reestablish. Costly transplant- greatest during the warmer times of specimen palms, understanding the ing failure rates can be 30% in some the year when soil and air temperatures seasonality of palm root growth, installations (Meerow, 1997). were highest. He suggested that palms how palm roots respond when trees Successful reestablishment of could be successfully transplanted at are dug, and the effects of canopy any season in tropical areas and south- manipulation during transplanting transplanted palms depends on rapid will enable them to adopt effective regeneration of roots, avoiding injury ern Florida because root and shoot and rational transplanting practices. and desiccation of the trees during growth in these warm humid climates This manuscript provides a review of transit and handling, and maintaining were frequent and regular year-round. research fi ndings that can be applied suffi cient soil moisture around the root He suggested that winter planting to maximize reestablishment of trans- balls after transplanting. Considerable was not advisable in cooler climates. planted specimen palms. resources and labor are spent in follow- However, published recommenda- ing SIPs intended to optimize these tions (Broschat and Meerow, 2000; factors, but there is a limited science Meerow and Broschat, 1992) advise ature palms are the em- basis to guide them. the optimum time for planting palms blematic signature plant of MMediterranean and tropical landscapes. They are important and conspicuous elements in landscapes of Arizona, California, Florida, Hawaii, and other warm-climate areas. Large specimen palms of several genera are in great demand and command premium prices in California and other areas, costing $30 to $400 per 12 inches (30.5 cm) of trunk height, depending on the species, plus several hundred dollars each to transport and install
University of California Cooperative Extension. 1Botany and Plant Sciences Department, University of California–Riverside, Riverside, CA 92521. 24800 Cesar Chavez Ave., Los Angeles, CA 91022. Fig. 1. The root initiation zone (RIZ) of a date palm (Phoenix dactylifera) off- 3669 County Square Dr., #100, Ventura, CA 93003. shoot.
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JJan2005HT.indban2005HT.indb 112828 112/6/042/6/04 4:36:074:36:07 PMPM in warm humid climates is during the However, the literature shows that generated relatively few. In the latter warm rainy season (June to October), most palms are able to generate new two species, however, the number of because plant growth is highest and root systems by the production of new cut roots that regenerated was high, rainfall is normally suffi cient to negate roots from the RIZ and/or branching even surpassing the number of new the need for supplemental irrigation. and regrowth of roots severed during roots originating from the trunk. In preliminary fi ndings, Hodel et transplanting. Based on their data, Broschat al. (1998) and Pittenger et al. (2000) Tomlinson (1961) stated that and Donselman (1984, 1990) recom- reported that root growth of many severed palm roots usually branch just mended that the distance from the palms generally tended to be highest behind the cut and continue grow- trunk at which 30% of the cut roots during the warmer months from spring ing. In Florida on fi eld-grown palms, regenerated should determine the through fall in southern California. Broschat and Donselman (1984, radius of the root ball. Thus, their rec- Recent fi ndings by D.R. Hodel (un- 1990) found that the response of roots ommended minimum root ball sizes, published) with fi eld-grown specimens to cutting varies among species. In measured in the radius from the trunk, of 16 palm species generally support recently completed fi eld research by were 6 to 12 inches (15.2 to 30.5 cm) the above reports, and demonstrate D.R. Hodel (unpublished), 16 species for queen palm, 12 to 24 inches (30.5 that winters in California (and regions showed varying degrees of branching to 61.0 cm) for mexican fan palm, with similar Mediterranean climates) and regeneration of severed roots with and at least 24 inches for senegal date are suffi ciently cool and long to reduce up to four branches per severed root. palm and royal palm, because there was root growth in most species. Their Branching and regeneration of severed little regeneration of roots cut shorter data further show the window of op- roots was prolifi c in certain species, than these lengths for the respective portunity for successful transplanting like canary island date palm, senegal species. Root balls for these last three is usually smallest in the fall and winter date palm (Phoenix reclinata), queen species are relatively large in order to and greatest in the late spring to early palm, windmill palm, miniature chusan encompass a suffi cient percentage of summer, but there were differences in palm (Trachycarpus wagnerianus), and roots that will branch and regenerate this pattern in a few species. Based on mexican fan palm, while it was minimal after being cut. their fi ndings, transplanting palms in in other species, such as pindo palm Hodel and Pittenger (2003) the fall and winter requires judicious (Butia capitata), mediterranean fan found similar results in date palm attention to other factors that affect palm (Chamaerops humilis), and scrub offshoots, where over two-thirds of transplant success, such as digging palmetto (Sabal etonia). new root growth was regeneration of and handling, planting depth, and ir- Digging the root ball is usually roots severed during removal from the rigation. Late spring to early summer done by hand or a combination of mother palm. The authors suspected transplanting might be especially criti- mechanical digging with a backhoe that many of the roots reported as cal for rare and/or unusually valuable and hand digging. However, there originating from the RIZ in earlier specimens or for any species that gener- is no generally accepted recommen- studies actually originated from sev- ate a preponderance of new roots in the dation for the optimal root ball size ered roots. summer. Thus, the literature indicates when transplanting large fi eld-grown Although specimen palms are the best time to transplant palms in palms. Recommendations range from mature enough to have a functioning southern California and similar Medi- nearly no root ball to one as big as RIZ, plant maturity can sometimes terranean climates is the late spring to possible (Broschat and Donselman, infl uence the functionality of the RIZ in early summer (May to July) because 1987; Hodel, 1997; Meerow and younger palms and, thus, impact their transplanting at this time provides a Broshat, 1992). Some investigators ability to regenerate roots after trans- long, warm period that promotes root have given much importance to the planting. Broschat (1990) determined growth and ensures the quickest and distribution of palm roots and their in pygmy date palm (Phoenix roebele- best establishment and survival. ability to branch and resume growth nii) and parlor palm (Chamaedorea when determining the optimal root elegans) that root regeneration from Palm root regeneration and ball size. In sengal date palm, royal the RIZ was dependent on the plant root ball size palm (Roystonea regia), queen palm, being mature enough for the trunk to Broschat and Meerow (2000) and mexican fan palm, Broschat and have reached its maximum diameter state that understanding how palm Donselman (1984, 1990) discovered and for the palm axis to have begun roots respond to digging is critical to some severed roots branched and elongating vertically. In contrast, root successful transplanting. Until recently regenerated from just behind the cut regeneration and RIZ function were it was widely believed that palm roots but, generally, the percentage of roots shown to be independent of these ma- cut during transplanting die and the that branched and continued growing turity indicators in date palm (Hodel tree must replace them with new pri- increased the farther the roots were and Pittenger, 2003), and overall root mary roots from the RIZ, thus justify- cut from the trunk. In coconut palm regeneration of juvenile plants was ing the rationale for digging a minimal (Cocos nucifera), about half of severed found to be abundant in transplanted root ball. Indeed, in palmetto palm roots regenerated regardless of the date palm, canary island date palm, (Sabal palmetto) nearly all cut roots distance from the trunk they were and queen palm (Hodel and Pittenger, die back to the trunk, meaning when cut. Furthermore, they found senegal 2003; Hodel et al., 2003). transplanted this palm has to generate date palm, royal palm, and mexican In practice, regenerating a large an entirely new root system from the fan palm produced high numbers of number of roots quickly is most critical trunk to establish successfully and sur- new roots from the base of the trunk, to successful transplanting of mature vive (Broschat and Donselman, 1984). while coconut palm and queen palm specimen palms, so the total number
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and density of new roots, rather than (1984, 1987, 1990). The pruning Root initials are often visible on their origin or a tree’s age, are the key purportedly stimulates a large number the bottom 6 to 12 inches of palm factors in determining the root ball of new roots to grow from the base of trunks in the area of the RIZ, and size. It is more important to take a the tree and a smaller root ball can be visible or hidden initials may exist 3 ft root ball only large enough to assure taken, but they provided no research- (0.9 m) or more higher on the trunk that a relatively large number of new based information to support the in some species (Broschat, 1995). roots is regenerated from any source practice. Even if root pruning provides Root initials above the RIZ do not rather than simply one large enough the positive benefi ts purported, there usually develop into functioning roots to ensure that a maximum number is serious concern with the practice in unless they are in contact with a moist of cut roots branch and continue that any new roots from the trunk or substrate (Tomlinson, 1990) or unless growing. In support of this concept, regenerated from branching of roots there is very high humidity maintained an important fi nding of Broschat and cut during root pruning will be highly by frequent rainfall or irrigation. Donselman (1984) and D.R. Hodel susceptible to damage during the Broschat (1995) showed that planting (unpublished) is that most of a mature digging, transporting, and replanting mature pygmy date palms more than palm’s roots are found within 12 inches processes. Recent recommendations 5.9 inches (15 cm) above the top of of the trunk. by Meerow (1997) and Broschat and the visible RIZ decreased tree survival Thus, another interpretation of Meerow (2000) seemed to place less and quality. These fi ndings suggest that the Broschat and Donselman data emphasis on root pruning but state it transplanting mature palms deeper (1984, 1990) is that a root ball with might be useful in some cases. than they were originally growing is a radius 6 inches out from the trunk While root-promoting substances not advisable, but it is impossible to would be suffi cient for nearly all the are known to increase root regenera- make defi nitive recommendations on species investigated because ≥50% of tion in dicotyledonous trees, research planting depth based on a study with all new roots regenerated, regardless on their use in palms indicates the one species. of origin, were found within that dis- application of auxin (indolebutyric In California, large specimens tance. More recent interpretations of acid) does not improve root initiation of mexican fan palm are sometimes these data by Meerow (1997), Meerow in a large number of species (Broschat, transplanted 3 to 6 ft (0.9 to 1.8 m) and Broschat (1992), and Broschat 1990). Thus, this practice is not recom- deeper than they were growing in and Meerow (2000) placed less em- mended or widely followed. their original location. However, the phasis on the ability of severed roots practice is controversial and not rec- to regenerate when determining root Planting depth ommended because death and decline ball size. These sources recommend a Landscape designs sometimes have been reported for many trees of root ball with a radius ≥8 inches (20.3 specify planting groups of mature palms this and other palm species planted in cm) larger than the trunk for trees at a uniform height, but it is often this manner. up to 15 ft (4.6 m) tall and a radius impossible for landscape contractors ≥12 inches larger than the trunk for to obtain multiple palms meeting the Leaf removal and leaf tie-up larger or multi-stemmed trees. For height requirement. Thus, a common During the transplant operation, palms where all the roots die back practice is to plant trees deeper than the SIP is to remove numerous func- to the trunk, such as palmetto palm, they were originally grown in the tional leaves, up to 75% of the existing they recommend digging a root ball nursery in order to meet the speci- crown, and tie up the remaining ones, only large enough to protect the RIZ, fi cation. There is very little research often for months after transplanting perhaps no more than a 6-inch radius documenting the effects of planting (Fig 2). These practices prevent dam- from the trunk. New data from D.R. depth on the survival and establishment age to the crown and apical meristem Hodel (unpublished data) suggest that of transplanted palms. during transport and handling, and a root ball 12 inches in radius from the trunk and 12 inches deep would be adequate for most palm species because this volume of soil typically includes ≥50% of the roots. A deeper root ball (≥24 inches deep) might be advanta- geous for pindo palm, chinese fountain palm (Livistona chinensis) and queen palm to ensure ≥50% of the roots are captured. Also, a deeper root ball might aid in stabilizing and anchoring any transplanted palm in situations where wind or other factors could cause it to lean or be unstable. Root pruning and root- promoting substances Root-pruning certain palms 1 to 3 months prior to transplanting was Fig. 2. Standard leaf tie-up and removal practice shown on recently transplanted suggested by Broschat and Donselman specimen canary island date palm (Phoenix canariensis).
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JJan2005HT.indban2005HT.indb 113030 112/6/042/6/04 4:36:094:36:09 PMPM they are purported by practitioners to palms, Hodel et al. (2003) found no ef- to keep large trees upright during the reduce water loss of the dug tree, which fect on tree survival after transplanting fi rst 6 to 12 months after transplant- improves the tree’s chances of survival, from various combinations of amounts ing in sites with frequent high winds and hasten its reestablishment. These of leaf removal with and without leaf (Broschat and Donselman, 1987). practices greatly disfi gure the crown tie-up. They failed to document any •Monitoring and management of newly transplanted specimen palms, reduction in transpiration or increase of insect pests (weevils and borers) reduce their functional attributes, and in leaf water potential in either spe- known to be attracted to stressed palms detract from their aesthetic value for cies from any treatment combination (Howard et al., 2001) months or years, yet there is limited either immediately after transplanting •Occurrence of root diseases research documenting the benefi ts of or during the following 6 months. when palm root balls are kept too either practice. In addition, no treatment resulted in wet, the site is poorly drained, or the Removing at least half the leaves greater numbers of new leaves or mass palm is planted too deeply (Donsel- and tying up the remaining ones have of new roots produced in either species. man, 1991). long been common practices when Based on their work with juvenile palms •Site selection and soil amend- severing offshoots of date palms from and earlier fi ndings of Broschat (1994) ment for palms (Broschat and Donsel- the mother tree and planting them and Reuveni et al. (1972), Hodel et man, 1987; Harris et al., 1999). out in the fi eld. Growers state this al. (2003) concluded that for most practice reduces water loss and facili- palms it is possible that little or noth- Conclusions tates handling. Nixon and Carpenter ing is gained from leaf removal and/or Available research indicates that (1978) and Zaid (1999), two of the tie-up during transplanting if the root specimens of most palm species can be best-known references on this subject, ball and backfi ll are kept moist. They successfully transplanted with a root recommend this practice. Reuveni et further stated there is doubt that these ball that is 12 inches in radius from the al. (1972) reported that less severe leaf SIPs are horticulturally sound except to trunk and ≥12 inches deep. The opti- removal of offshoots did not improve facilitate moving and minimize dam- mum time to transplant most specimen rooting when planted in the traditional age to the crown and apical meristem palms in southern California and areas manner, but offshoots retaining all during the transplanting procedure. In with similar Mediterranean climates is their leaves had higher rooting with an ongoing follow-up study by these the late spring to early summer (May to overhead misting. authors (D.R. Pittenger, unpublished), July), while in warm, humid, tropical Broschat (1991) and Costonis it appears that leaf removal and tie-up areas such as southern Florida it is best (1995) showed that for species like do not improve survival or reestablish- to transplant palms in the rainy season the palmetto palm, which must gener- ment of california fan palms having 6 (June to October). If post-planting ate an entirely new root system when to 10 ft (1.8 to 3.0 m) of trunk, which irrigation is available, palms could be transplanted, complete leaf removal supports the authors’ published fi nd- successfully transplanted at any season greatly improved survival rates because ings for juvenile palms. in warm, humid, tropical areas and the practice reduced transpirational wa- southern Florida. ter loss. Conversely, Broschat (1994) Irrigation Root-pruning palms in advance of showed that transplanted pygmy date The importance of keeping digging them for transplanting has no palms had higher new root and shoot the root ball and backfi ll soil of a proven benefi t, and the practice may growth and survival rates when most transplanted palm well watered was result in serious damage to any newly or all leaves were left on the palm, documented for pygmy date palm developed primary or regenerated provided there was suffi cient irrigation. by Broschat (1994), who found that roots during the digging, transporting, He predicted that most other species regular irrigation improved plant sur- and replanting processes. Similarly, the of palms would probably respond vival, plant quality, and root growth. use of root-stimulating hormones is similarly to the pygmy date palm, and In addition, he showed that placing not benefi cial in palms. he recommended that leaves should sprinklers directly in the crowns (foliar When transplanting a palm, re- be untied after transplanting because misting) of transplanted palms was not search suggests it is important to set the research had shown no benefi t from as benefi cial as applying water directly tree so that its RIZ is at the same depth the practice in humid climates. He to the soil. Hodel et al. (2003) also at which it was originally growing. further suggested leaf tie-up promotes suggested the value of keeping the Planting a palm with the RIZ buried disease by decreasing air fl ow through root ball moist in their leaf removal ≥6 inches below grade can cause tree the canopy, but in arid climates there and tie-up studies with canary island decline or death, while planting a tree might be some benefi t from keeping date palm and queen palm. with the RIZ too high above grade can the leaves tied up for several weeks to reduce root regeneration. reduce transpirational water loss. Re- Other practices The SIP of removing a large num- cently, Broschat and Meerow (2000) There are other industry practices ber of leaves and tying up remaining recommended that one-half to two- and factors sometimes associated with ones during transplanting is probably thirds of the leaves should be removed transplanting specimen palms that are useful in preventing damage to the to minimize transpirational water loss discussed in the literature but for which crown and meristem during the op- in large, specimen-sized, fi eld-grown there is no research-based information eration, but there is little evidence the palms but they did not cite support- pertaining to their infl uence on or ef- practice enhances survival and reestab- ing data. fectiveness in successful transplanting. lishment of the tree. It may be best, In a recent study with juvenile These include: both horticulturally and aesthetically, canary island date palms and queen •Use of bracing or other support simply to remove only the older dead
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leaves, tie up the remaining crown until Hodel, D.R. 1997. Planting palms. the palm is relocated in the new site, and Grounds Maintenance 32:C10–12. A Review of then untie the crown immediately. Care Hodel, D.R., A.J. Downer, and D.R. Pit- the Effects of should be taken to protect the root ball tenger. 1998. Palm root regeneration, p. from physical damage and desiccation 46–50. In: D. Neeley and G.W. Watson Transplant Timing during the transplanting process, and (eds.). Proc. Intl. Wkshp. Tree Root De- the backfi ll around the new transplant velopment in Urban Soils. The Landscape on Landscape should be kept uniformly moist until Below Ground, II. Intl. Soc. Arboricult., the plant is established. Champaign, Ill. Establishment Hodel, D.R. and D.R. Pittenger. 2003. Literature cited Studies on the establishment of date of Field-grown Broschat, T.K. 1990. IBA, plant maturity, palm (Phoenix dactylifera ‘Deglet Noor’) Deciduous Trees in and regeneration of palm root systems. offshoots. Part I: Observations on root HortScience 25:232. development and leaf growth. Palms 47(4):191–200. Temperate Climates Broschat, T.K. 1991. Effects of leaf removal on survival of transplanted Sabal palms. J. Hodel, D.R., D.R. Pittenger, and A.J. 1 Arboricult. 17:32–33. Downer. 2003. Effects of leaf removal and Lisa E. Richardson-Calfee tie up on juvenile, transplanted Canary Broschat, T.K. 1994. Effects of leaf re- Island datepalms (Phoenix canariensis) and J. Roger Harris2 moval, leaf tying, and overhead irrigation and queen palms (Syagrus romanzoffi ana). on transplanted pygmy date palms. J. Palms 47(4):177–184. Arboricult. 20:210–213. ADDITIONAL INDEX WORDS. fall, root Howard, F.W., D. Moore, R.M. Giblin- growth, root regeneration, season, Broschat, T.K. 1995. Planting depth af- Davis, and R.G. Abad. 2001. Insects on spring, summer fects survival, root growth, and nutrient palms. CABI Publ., New York. content of transplanted pygmy date palms. SUMMARY. Prudent landscape profes- HortScience 30:1031–1032. Meerow, A.W. 1997. Betrock’s guide to sionals can enhance chances for suc- landscape palms. Betrock Info. Serv., Hol- cessful establishment by timing tree Broschat, T.K. 1998. Root and shoot lywood, Fla. transplant operations to coincide with growth patterns in four palm species and Meerow, A.W. and T.K. Broschat. 1992. ideal seasonal conditions. However, their relationships with air and soil tempera- transplant timing is usually deter- tures. HortScience 33:995–998. Transplanting palms. Coop. Ext. Serv. Circ. 1047. Univ. of Florida Inst. of Food and mined by economic factors, resulting Broschat, T.K. and H.M. Donselman. Agr. Sci., Gainesville. in trees being transplanted at times 1984. Regrowth of severed palm roots. J. that are unfavorable for their sur- Arboricult. 10:238–240. Nixon, R.W. and J.B. Carpenter. 1978. vival and growth. Knowledge of the Growing dates in the United States. U.S. effects of season of transplanting on Broschat, T.K. and H.M. Donselman. Dept. Agr. Info. Bul. 207, Washington, the establishment of landscape trees 1987. Factors affecting palm transplant- D.C. can help assure the highest probabil- ing success. Proc. Fla. State Hort. Soc. ity of success, especially since special Pittenger, D.R, A.J. Downer, and D.R. 100:396–397. post-transplant management may be Hodel. 2000. Palm root regeneration required if trees are transplanted at Broschat, T.K. and H. Donselman. 1990. and its signifi cance in transplanting. In: unfavorable times. This manuscript Regeneration of severed roots in Wash- T.G. Ranney (ed.). Metropolitan Tree reviews past and current research on ingtonia robusta and Phoenix reclinata. Improvement Alliance (METRIA). Proc. the effects of transplant timing on Principes 34(2):96–97. 11th METRIA Conf. 20 Apr. 2004. landscape establishment of deciduous
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