Water is the most limiting factor in establishing container-grown trees and shrubs in the landscape, and water stress is the number one cause of transplant failure (Barnett, 1986; Gilman et al., 1996). Irrigation and water management are important components of the urban landscape as demand for plants, population expansion, and increased housing starts have escalated concerns among water management officials that requests will exceed supply (Archer, 2002). Landscape water consumption is highly visible and provides a prime target for water restrictions and subsequent regulation (Salamone, 2002; Thayer, 1982). Imposing water restrictions during landscape establishment can be detrimental to plants that have not had adequate time to develop sufficient root systems to compensate for losses to evapotranspiration (Montague et al., 2000). Because retail nurseries offer guarantees against plant death during the first year after purchase, plant death resulting from insufficient water for establishment can have a significant economic impact on the nursery industry.
Current recommendations and regulations in Florida vary by source and municipality and often do not correspond. Recommendations advise daily irrigation until established with establishment times increasing proportional to container size. References indicate standard 3-gallon containers commonly used in both residential and commercial landscape installations require 6 to 12 months to establish, yet recent trends within Florida have been toward the adoption of policies such as 60 d or less of daily irrigation for landscape establishment (Trenholm et al., 2002). Furthermore, irrigation recommendations and estimated establishment rates are based primarily on anecdotal observations of plant performance of mixed landscape plantings (Garcia-Navarro et al., 2004).
Many factors, including application frequency, are known to affect shrub establishment, yet there are no clear data on how long it takes for a shrub to become established. Daily irrigation of Ilex cornuta ‘Burford Nana’ during establishment significantly increased shoot number, shoot-to-root ratios, and the percentage of roots originating from the top half of the root ball. Less frequent irrigation promoted deeper rooting but decreased shoot growth (Gilman et al., 1996). No differences in mortality rates or aesthetic quality were found between irrigation frequencies of Ceanothus griseus (Trelease) McMinn var. horizontalis ‘Santa Ana’, Rhamnus californica Eschscholtz, R. californica ‘Eve Case’, and Photinia ×fraseri Dress provided the total volume of water applied was equal and within the tolerance of the species (Paine et al., 1992). Establishment times for various tree species have been determined based on leaf gas exchange, water potential, and growth parameters; however, the methodology has not been applied for determination of shrub establishment rates (Beeson and Gilman, 1992; Montague et al., 2000; Watson, 1985). Given the discrepancies between irrigation regulations and recommendations and a lack of viable knowledge regarding shrub establishment rates, the objectives of this study were to determine 1) the effects of irrigation frequency on establishment, growth, and aesthetic quality of Ilex cornuta ‘Burfordii Nana’, Pittosporum tobira ‘Variegata’, and Viburnum odorotissimum and 2) quantify the time until establishment.
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