Answer: It depends on which kind of cedars you have. Red cedar (Juniperus) or white cedar (Thuja).
Early spring, before new growth begins is a good time to trim
arborvitae. The flush of new growth will fill in any bare areas
uncovered by pruning.
When trees are young, you can remove a great amount of wood with no ill effect. As they mature you should remove less and
less. Never remove more then 1/3 of a tree or shrub at any time, and never cut the entire top off of a tree (or let a tree service,
either!). Topping causes a flush of new growth which severely weakens the tree. This makes it all the more susceptible to
damage from pests and disease. Use crown reduction pruning and thinning instead, and do not remove more then 1/3 of the
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