Arboriculture & Urban Forestry 33(3): May 2007 207 1992). If RH is low (like in a semiarid climate), there is greater evaporative demand and many species respond by partial stomatal closure (Montague et al. 1998), which de- creases GS, water loss, and photosynthetic rate. In climates with increased RH, evaporative demand placed on plants is generally less when compared with evaporative demand placed on plants in arid or semiarid climates (Montague et al. 1998, 2000a). Therefore, plants in our study (in a climate with high RH) were likely subjected to lower evaporative demand throughout the day. This response in combination with benefits of organic mulch (increased soil moisture, mod- erate soil temperatures, and so on) likely allowed plants over mulch to have greater GS, water loss, photosynthetic rate (Hinckley et al. 1978), and growth when compared with plants grown without the benefits of organic mulch. Water requirements of landscape plants have been esti- mated over several years and by various methods (Sachs et al. 1975; Paine et al. 1992; Montague et al. 2004; Shaw and Pittenger 2004). Montague et al. (2004) found total daily ETO taken over an extended period of time to be a limited but valuable tool to estimate water needs of recently transplanted tree species. This appears true for plant species used in this study. We found shrubs irrigated at 75% ETO produced gas exchange and growth generally similar to shrubs irrigated at the 100% ETO level (Figures 2–5). Of species tested, only forsythia transplants irrigated at the 100% ETO level had greater gas exchange and growth when compared with trans- plants irrigated at the 75% ETO level (Figure 4). Lockett et al. (2002) reports several ornamental species previously established in the landscape [pink evening prim- rose (Oenothera speciosa), prairie verbena (Verbena bipin- natifida), red yucca (Hesperaloe parviflora), ceniza (Leuco- phyllum frutescens), and ruellia (Ruellia nudiflora)] irrigated over the growing season at 60% ETO had acceptable appear- ance and growth. Shaw and Pittenger (2004) investigated aesthetic quality of 30 ornamental species (also previously established in the landscape) planted into landscapes and ir- rigated at three irrigation levels (36%, 18%, and 0.0% ETO). They found many of the species performed well (high aes- thetic quality) at the 36% and 18% ETO irrigation levels. Although not statistically analyzed, we found after one grow- ing season all plants (regardless of species, irrigation level, or mulch treatment) had aesthetic qualities that would likely be acceptable in landscape situations (Lockett et al. 2002). CONCLUSIONS Planting containerized crapemyrtle, spirea, and photinia plants in landscape beds with mulch and irrigating at the 75% ETO irrigation level produced similar gas exchange and growth as transplants grown with mulch and irrigated at the 100% ETO irrigation level. However, during the growing season, irrigation at the medium rate conserved over 1,700 L (450 gal) of water. Compared with the high irrigation rate, forsythia transplants had lower gas exchange and growth at the low irrigation rate. In general, planting with mulch ap- peared to increase gas exchange and growth of all transplants. Although all transplants performed well at greater irrigation rates, we found using organic mulch and irrigating during the initial growing season at 50% ETO produced plants with acceptable growth and aesthetics for landscape situations. These findings should be useful for landscape irrigation scheduling and for incorporating water conservation into landscape maintenance programs. Acknowledgments. Support for this project was provided in part by a grant from the College of Agricultural Sciences and Natural Re- sources, Texas Tech University. Manuscript No. T-4-577 of the College of Agricultural Sciences and Natural Resources. Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the author or Texas Tech University and does not imply its approval to the exclusion of other products or vendors that also may be suitable. LITERATURE CITED Allen, R.G. 2000. REF-ET: Reference evapotranspiration cal- culation software. Windows Version 2.01.17. Department of Biological and Agricultural Engineering, University of Idaho, Moscow. Arnold, M.A., G.V. McDonald, and D.L. Bryan. 2005. Plant- ing depth and mulch thickness affect establishment of green ash (Fraxinus pennsylvanica) and bougainvillea goldenraintree (Koelreuteria bipinnata). Journal of Arbo- riculture 31:163–170. Costello, L., and J.L. Paul. 1975. Moisture relations in trans- planted container plants. HortScience 10:371–372. Ferguson, B.K. 1987. Water-conservation methods in urban landscape irrigation: an exploratory overview. Water Re- sources Bulletin 23:147–152. Fraedrich, S.W., and D.L. Ham. 1982. Wood chip mulching around maples: effect on tree growth and soil character- istics. Journal of Arboriculture 8:85–89. Greenly, K.M., and D.A. Rakow. 1995. The effect of wood mulch type and depth on weed and tree growth and certain soil parameters. Journal of Arboriculture 21:225–232. Hensley, D.L., R.E. McNiel, and R. Sundheim. 1988. Man- agement influences on growth of transplanted Magnolia grandiflora. Journal of Arboriculture 14:204–207. Hild, A.L., and D.L. Morgan. 1993. Mulch effects on crown growth of five southwestern shrub species. Journal of En- vironmental Horticulture 11:41–43. Hinckley, T.M., R.G. Aslin, R.R. Aubuchon, C.L. Metcalf, and J.E. Roberts. 1978. Leaf conductance and photosyn- thesis in four species of the oak-hickory forest type. For- est Science 24:73–84. Jensen, D.T., G.H. Hargreaves, B. Temesgen, and R.G. Allen. 1997. Computation of ETO under non-ideal conditions. ©2007 International Society of Arboriculture
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