WORKSHOP 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 Time of year to transplant and Ellis Farms (Borrego Springs, Ca- and seasonality of palm root Specimen Palms: lif.); unpublished].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. 128 ● January–March 2005 15(1) JJan2005HT.indban2005HT.indb 112828 112/6/042/6/04 44:36:07:36:07 PPMM 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