Pruning Roots Affects Tree Quality in Container-Grown Oaks

Abstract

Height and trunk growth of Quercus virginiana ‘SDLN’ Cathedral Oak® tops was not affected by root pruning that occurred each time trees were potted into a larger container, beginning when rooted cuttings were planted into #3 containers. All trees produced in air root-pruning Accelerator® containers without mechanical root pruning produced enough circling roots to make them culls according to Florida and California standards for nursery stock. Removing root defects by pruning roots when trees are potted to the next larger size reduced culls from 100% to 40% of the crop and is recommended for quality tree production. Root pruning when trees were potted from one container size to the next size had no influence on the number of primary structural roots that grew directly from the trunk base. Root pruning had no impact on the number of roots that were deflected down. Waiting to root prune until #3 containers were potted into #15 containers did not increase the number of straight roots compared to non-pruned controls. Slicing the root ball edges vertically from top to bottom in several places appears to reduce circling roots capable of forming stem girdling roots. But slicing in the manner described in this study did little to reduce the descending root defects.

Effect of Eight Container Types and Root Pruning During Nursery Production on Root Architecture of Acer rubrum

“…Direct comparisons are difficult to make among the studies, but shaving the root ball likely removed more of the root system than slicing and teasing because shaving severs every root that reaches the periphery of the root ball. This demonstrates, as others have shown (Gilman et al 2009;Gilman et al 2010b), that root architecture can be improved by root-ball shaving container-grown shade trees receiving regular irrigation in the nursery without slowing their growth.…”

Effect of Liner Container Size, Root Ball Slicing, and Season of Root Pruning in a Field Nursery on Quercus virginiana Mill. Growth and Anchorage After Transplanting

“…Root remediation by slicing root balls and removing potentially girdling roots on the top of the liner root ball had little influence on post-transplanting xylem potential, trunk diameter, or tree height; this was also found in other taxa planted from nursery containers (Gilman and Masters 2010;Harris and Day 2010). However, root pruning by slicing the root ball when planting containers into the field nursery increased root system quality in the current study and others (Gilman et al 2009); despite this increase, 66% of trees at the end of the field production period graded as culls, and an average of 43% of trunk circumference remained circled on trees receiving the slicing treatment (Table 2). This data combined with others (Gilman et al 1996;Weicherding et al 2007;Gilman and Masters 2010) calls into question the effectiveness of shallow root ball slicing.…”

“…In contrast, there was no impact of container size on percentage of trunk circled with roots >5 mm diameter (54%) or percentage of trees graded as root culls (76%), according to Florida Grades and Standards for Nursery Plants (Anonymous 1998). Other studies have also found a high percentage of trees to be graded as root culls (Gilman et al 2009). Root pruning by slicing root balls prior to planting into the field nursery impacted root attributes and anchorage when trees were harvested from the field nursery at the end of 2009 (Table 2).…”

“…Gilman et al (1996) showed that shallow (2 cm deep) vertical slicing (often called scoring) from top to bottom on larger (11 L) root balls of Burford holly (Ilex cornuta 'Burfordii'), when planting to field soil, resulted in a redistribution of roots, not an increase in roots compared with non-pruned controls. Scoring 11 L container root balls on Q. virginiana as they were shifted into 57 L containers resulted in an improvement in root system quality (Gilman et al 2009). Despite these experiences, there were no reports of employing root ball scoring on container liners used for establishing a field nursery and how that might influence landscape transplanting or anchorage.…”

Nursery Planting Depth, Mulch Application, and Root Pruning at Landscape Planting Affect Tree Health and Anchorage

“…Removing defects by pruning roots when trees of at least nine taxa were shifted to the next larger size dramatically reduced number of trees grading as culls (Anonymous 1998) in nursery containers (Harris et al 1971a;Harris et al 1971b;Gilman et al 2009;Gilman et al 2010c). Growing in certain container types can also improve quality by reducing root deflection (Gilman et al 2010a;Gilman and Paz 2014).…”