Cut-off in their prime? Response of two landscape shrubs to different levels of root pruning, during active and quiescent growth phases

Shrubs have an important role in the future design of urban landscapes. Due to city-densification and pressure on space, shrubs are increasingly preferred over trees for urban amenity plantings. In contrast to trees, however, relatively little information exists on how shrubs adapt to urban stress. This includes their responses to physical root injury, that might occur through trenching or transplanting activities. Two shrub taxa, Philadelphus coronarius ‘Aureus’ and Euonymus fortunei ‘Silver Queen’, were used to investigate the effects of severity and time of root injury on plant viability, and how additional fertiliser influenced recovery. A novel ‘split-pot’ system was developed to differentiate where root injury was induced. Results showed that both taxa were relatively resilient to root-pruning, although root injury was more detrimental during active growth than when plants were quiescent. This re-enforces the notion that transplanting of shrubs should be avoided in the summer. Shoot development was not more detrimentally affected by severe root-pruning compared to light pruning. There was also evidence that uniform severe pruning across the root-ball stimulated stronger root-regeneration compared to root systems differentially injured. No consistent response to fertiliser was noted. Results have implications for the resilience and management of shrubs within the urban landscape.