Hedge shaping and size maintenance is often accomplished with electric or gas-powered shears due to a lower cost compared to hand pruning. Shearing plants arbitrarily removes the apical growing points from external portions of the shrub to achieve a desired shape and size of the plant and often results in poor quality cuts, leaving ragged ends of woody tissues or leaves. Contrarily, hand pruning makes strategic, ‘clean’ cuts often back to lateral branches to achieve these goals. Use of plant growth regulators like paclobutrazol (PBZ) can reduce the frequency of pruning and could be a useful component of a hedge management program. The purpose of this study was to investigate the effects of shearing, hand pruning, and/or PBZ application on regrowth of foliage and non-structural carbohydrates (NSCs) of ‘Winter Gem’ boxwood over time. Fifteen shrubs each per pruning type x frequency combination were pruned with bypass hand pruners (hand pruned) or gas-powered shears (sheared) in 2021, 2022, and 2023 once or twice per growing season. In addition, another 15 shrubs each were sheared once followed by an immediate application of a foliar PBZ (i.e. Trimtect®) in accordance with the label using an electric backpack or left as non-pruned controls. In 2021 and 2022, shrubs were pruned by removing 15 percent of the overall height and 20% of the overall widths in two perpendicular directions of each shrub. In 2023, pruned shrubs were cut back to the previous season’s overall height and width. Regrowth was measured by weighing the fresh biomass removed at each pruning and NSCs were measured from ten woody twigs from the exterior of each shrub using the phenol-sulfuric acid quantification method. Two and three years after pruning, shearing shrubs twice had significantly more biomass produced year over year compared to hand pruning, while PBZ treated shrubs had the least amount of regrowth. NSCs trended to be highest in shrubs that were hand pruned once or in PBZ treated shrubs, while the least in shrubs that were sheared twice. PBZ-treated shrubs had tighter clusters of internodes resulting in approximately 30% reduction in stem elongation compared to controls. The differences in growth dynamics and carbon storage across these different pruning strategies can have different long- and short-term implications in managing boxwood hedges, which will be presented here.
