166 O'Connor et al.: Container Type Affects Root Development During Landscape Establishment Alm 1983; Gilman and Harchick 2014; Gilman et al. 2015). Roots deflected in plastic containers grow in many directions, causing constrictions and circling roots (Gilman et al. 2010a) and uneven root development (Marler and Davies 1987). Malformed roots that begin with con- tainer production can later lead to instability and possible tree failure (Lindström and Rune 1999; Gilman and Paz 2014; Gilman et al. 2015). Because of the potential problems associated with plant production in BP containers, alter- native container types have been developed, including those with air root pruning technology, bottomless containers, fabric containers, contain- ers incorporating chemical compounds, and con- tainers using mechanical deflection technology. Some researchers have observed fewer circling/ girdling roots with alternative containers (Arnold and Struve 1989; Beeson and Newton 1992; Struve et al. 1994; Martin and Bhattacharya 1995; Marshall and Gilman 1998; Gilman 2001). Fabric containers may reduce the occurrence of cir- cling roots because of the “air pruning” effect on roots intercepting the container wall (Jones 1987; Langlinais 1987; Reese 1987; Privett and Hummel 1992; Marshall and Gilman 1998; Gil- man et al. 2010a), which stimulates secondary root branching and discourages root circling. Nursery production studies examining the effects of container type on root and/or shoot growth have yielded mixed results. While some have found few differences in aboveground growth among various container types (Marshall and Gilman 1998; Owen and Stoven 2008; Neal 2009), O’Connor et al. (2013) found that Callery pear trees grown in fabric containers grew more in height and stem caliper than trees grown in BP containers after two years. Conversely, Ortega et al. (2006) found that pine trees grown in air-pruning containers had slower root and canopy growth. Few studies have examined effects of container type on growth aſter planting in the landscape. Marshall and Gilman (1998) and Gilman et al. (2003), working with low-profile, air root-pruning containers, found increased caliper growth on red maple (Acer rubrum L.) roots five years aſter plant- ing. Gilman et al. (2015) found that circling roots of container-produced Ulmus and Acer persisted for as long as five years aſter landscape planting. ©2018 International Society of Arboriculture The current study examined container effects on root and shoot growth of Chanticleer® pear, pro- duced in the nursery using three container types (black plastic, Root Pouch®, and Smart Pot®), and for three years following planting in the landscape. MATERIALS AND METHODS Nursery Planting Two-year-old, lightly branched bare-root whips of Pyrus calleryana ‘Glen’s Form’ (Chanticleer) were planted into three container types on 07 May 2010 at the Colorado State University Plant Envi- ronmental Research Center (PERC), Fort Collins, Colorado, U.S. (USDA hardiness zone 5a) (40.56N, 105.08W). Prior to planting, roots were rehy- drated by soaking in water for 30 minutes. Trees were root pruned to eliminate broken or crossing roots. The three container types used were: a) #15 standard black plastic container (BP) (Lerio Corp., Mobile, Alabama, U.S.), b) #15 fabric container (RP) (Root Pouch, Averna & Associates, Hillsboro, Oregon, U.S.), and c) #15 fabric container (SP) (Smart Pot, High Caliper Growing, Inc., Oklahoma City, Oklahoma, U.S.). The container substrate (pH of 6.8, EC of 3.7 mmhos/cm) was a locally produced nursery mix (Organix Supply, Inc., Plat- teville, Colorado, U.S.), which consisted of 40% composted wood products, 40% sphagnum peat moss, 10% dehydrated poultry waste, 5% bark fines, and 5% volcanic pumice by volume. Aſter planting, trees were fertilized by topdressing each container with 250 g of Osmocote Pro® 19N–2.1P– 6.6K (The Scotts Company, Marysville, Ohio, U.S.). At planting, trees averaged 17.7 mm (SE ± 2.8 mm) in trunk caliper (diameter), measured at a point 15 cm above soil line and 161.4 cm (SE ± 17.1 cm) in height. Containers were placed on the ground on black woven cloth in three rows with 0.9 m spacing within rows and 1.8 m spac- ing between rows. Trees were attached by a 1.8 m bamboo stake to a wire trellis 1.2 m above ground to prevent them from blowing over. Trees were placed in a randomized complete block design, with five single-plant replicates per con- tainer type. Trees were pruned to correct branch- ing structure and to remove damaged branches. During the nursery establishment phase (first six months aſter planting in containers), trees
July 2018
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