Consumers consider plant quality an overwhelmingly important factor when purchasing landscape plants (Brand and Leonard, 2001; Khatamian and Stevens, 1994). Quality considerations include dark green foliage (Baker, 1965), evidence of new growth, and absence of discolored or damaged leaves (Brand and Leonard, 2001). There is little evidence that indicates consumers pay attention to root ball condition at purchase, yet landscape establishment is affected by the condition of root systems at transplant. Arnold and Struve (1989) and Struve (1993) report delayed landscape establishment when transplanting container-grown plants with overly developed (i.e., root-bound) root systems. The most critical factor affecting landscape establishment appears to be root growth (Watson and Himelick, 1997) and rapid expansion of roots (Blessing and Dana, 1987; Woods, 1959) into surrounding soil.
Landscape service providers and homeowners often manipulate root balls when installing landscape plants to promote root development and correct circling roots, yet evidence supporting or refuting the practice is mixed. Shoot and root growth of european white birch (Betula pendula) decreased with progressive root removal (Bellet-Travers et al., 2004). Pre-transplant root pruning stimulated shoot and root growth for southern magnolia (Magnolia grandiflora) the first year in a landscape (Gilman, 1992), yet Farmer and Pezeshki (2004) reported adverse affects on height among seedling nuttall oaks (Quercus nuttalli). Root pruning had no effect on trunk growth or height of pecan (Carya illinoinensis) (Wood, 1996) nor shoot or root growth of ‘Radiant’ crabapple (Malus ×hybrida) (Schnelle and Klett, 1992).
Gilman et al. (1996) reported that with daily irrigation, slicing of root balls did not affect shoot or root growth in ‘Burdfordii Nana’ holly (Ilex cornuta) 4 months after transplanting into a landscape. Mechanical root disruption of container-grown ‘Sea Green’ juniper (Juniperus chinensis) produced greater dry weight of new roots but less shoot growth than undisturbed root balls in loam soil. However, in clay soil, root ball manipulations reduced new root growth (Blessing and Dana, 1987).
Objectives of this research were 1) to evaluate the effect of root ball conditions at transplanting on canopy growth and biomass production and 2) to determine if root ball slicing is beneficial during landscape establishment of plumbago.
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