Arborvitae is an evergreen plant grown as a tree or shrub in Eastern Canada and the Northeastern United States. Like many evergreens, arborvitae needs very little pruning care to train the plant. Pruning goals for an arborvitae should focus on restoring the tree's vigor, removing damaged limbs or thinning the canopy to improve light and circulation. Pruning an arborvitae should be planned carefully before you remove any limbs. Unlike deciduous trees, an arborvitae will not regrow canopy that has been removed.
Mix a solution to sterilize your tools that consists of one part bleach and nine parts water. Saturate a clean cloth with this solution and wipe the blades of your tools. Continue to clean your tools with this solution in between pruning arborvitae trees and after removing individual diseased limbs in order to halt the spread of diseases.
Prune your arborvitae tree after first planting it to bring the canopy down to a size that is small enough for the rootball to support. Many arborvitae trees are grown in nurseries in the ground and then dug up for planting. During this process, growers may remove a large portion of the tree's roots. After planting the arborvitae, prune the tree's canopy so that it is the same size as the rootball or smaller so that the tree will thrive.
Remove weak limbs, closely spaced branches, limbs with weak forks or limbs that grow inward from your tree with pruning shears or branch loppers while they are small and the tree is young and vigorous. An arborvitae will recover from pruning better when it is smaller than after it grows large. Once an arborvitae is trained, it will need very little pruning. Use pruning shears to remove twigs that are smaller than a pencil in diameter. Use branch loppers for larger limbs.
Run your hands along the branches of your arborvitae to identify the dead zone of the tree before pruning. The dead zone is the interior of the tree in which light will not penetrate. You must prune your arborvitae only in the live zone region outside this dead zone. Vegetation will never grow in the dead zone. If you prune the arborvitae to the point that the dead zone is exposed, the tree will always appear bare.
Remove limbs that are dead, back to the trunk of the arborvitae. Trim the limb off starting at the point just outside the growth ring where the limb meets the trunk and slope downward at a 45-degree angle away from the tree.
Cut diseased or broken limbs back to the first healthy live shoot that offshoots the limb in the live zone. Cut the limb straight across at a point just above the shoot or bud. If the branch is broken or diseased down to the dead zone, remove the limb back to the trunk of the tree.