Arborvitae, belonging to the genus Thuja, are popular evergreen trees and shrubs valued for their dense, scale-like foliage, making them highly effective for privacy screening and formal landscaping. To maintain a full, healthy appearance and characteristic shape, proper pruning technique and timing are essential. Understanding the plant’s growth cycle is the most important factor in determining the correct schedule for any pruning activity.
Seasonal Timing for Routine Maintenance
The optimal window for light shearing, shaping, and maintaining a dense hedge is from late spring to early summer. This timing follows the plant’s initial surge of spring growth, typically occurring from late May through June. Waiting until this growth flush has matured slightly allows the new shoots to be trimmed back, creating a tight, formal exterior.
Trimming at this point encourages the arborvitae to produce more lateral growth, creating a thick, dense wall. The fresh, bright green growth that emerges after the cut quickly conceals the trimmed ends, giving the hedge a clean, uniform look. This light, frequent trimming is necessary to prevent the plants from becoming overgrown and thin. If a second, light cleanup is needed, complete it by mid-July to ensure the plant has sufficient time to prepare for the dormant season.
Timing for Major Structural Pruning
Structural reduction, involving heavy cuts to reduce overall size or remove significant dead or diseased wood, should be scheduled during the plant’s dormant period. This period falls in late winter or very early spring, typically before the new buds begin to swell. Pruning an evergreen when it is dormant minimizes the physiological stress placed on the plant.
Cutting while the arborvitae is inactive helps reduce sap loss and allows the plant to allocate stored energy reserves toward healing wounds and supporting new growth once spring begins. When making structural cuts, remember the “no green, no grow” rule unique to arborvitae. Cutting back into old, brown wood where there is no visible green foliage will create a permanent, bare gap because Thuja species do not possess dormant buds that allow them to regenerate.
Critical Times to Avoid Pruning
Pruning should be avoided from late summer through the fall season, as this practice can compromise the plant’s winter hardiness. Trimming after mid-August stimulates a flush of new, tender growth that will not have enough time to “harden off” before the first hard frost arrives. This immature growth is susceptible to winter burn and desiccation, which can damage the branches and weaken the plant.
Avoid pruning during periods of environmental stress, such as extreme heat or prolonged drought. When the arborvitae is already struggling to manage water loss and maintain basic functions, introducing the stress of pruning can be detrimental to its recovery and overall health. Similarly, heavy pruning immediately after a strong application of fertilizer should be avoided, as the combined stimulus can force out tender growth at an inappropriate time of year.