The northern white cedar (Thuja occidentalis) is also known as eastern arborvitae, American arborvitae, eastern white-cedar, swamp-cedar, and Atlantic red cedar. This lovely evergreen is generally used as a dense hedge in landscape design, it is also a low maintenance, fast growing planting. Normally, it requires very little pruning. Pruning an overgrown white cedar hedge will be somewhat of a challenge (depending upon the degree that it is overgrown). You must shear the hedge to the desired size and space within your landscape.
Shear the white cedar hedge in the early spring through the end of July (most heavy pruning should be done in mid summer – that way you will not be removing any old/inner wood). Do not prune later in the year, as branches will not have time to produce new growth.
View the hedge and locate the shortest plant. This will act as a guide when it comes to height.
Shear the top of the hedge to the height of the shortest plant using your hedge trimmers. Normally, you would only remove 3 inches of growth. If you need to remove more than that due to the degree of over-growth, do it slowly throughout the spring/summer to see how the hedge reacts. Severe pruning can be hard on the plant, and you could cause irreparable damage. Shearing will promote new growth, which will sprout from the old wood forming a dense hedge.
Shear the sides of the hedge, keeping the top narrower than the bottom. This allows winter snow to fall off the top of the hedge without breaking the branches, and there is fullness at the bottom of the hedge (plant trunk/stems are not exposed).