White Cedar, known botanically as Thuja occidentalis, is an evergreen tree with scaly, flattened foliage in a hue of bright to mid-tone green. The trees are slow-growing, like many evergreens, and reach roughly 40 feet in height and 12 feet in spread at maturity. The canopy has a softened pyramid shape that is symmetrical and naturally tidy in appearance. According to the University of Florida, they require little to no pruning save the removal of damage or when grown as shaped hedging.
Remove dead, damaged, diseased or otherwise compromised foliage and branches when you see them. Prune only what must be removed in order to get back to healthy tissue. Holes in the foliage will be slow to fill in, so make individual cuts, twig by twig and branch by branch, carefully excising the problem spots and leaving as much foliage in place as possible.
Correct any outlying, non-symmetrical outgrowths of foliage by shearing the branch tips down to restore a smooth line and symmetry to the canopy. Hold the pruning shear blades roughly parallel with the plane of the canopy as you cut to maintain a smooth line and prevent gouging into the foliage.
Shear, prune and shape the sides and top of your white cedar only if you intend to maintain this pruning regimen over the long term. Once topped, white cedar will not be able to fully restore the pyramidal shape. Hold the long pruning blades parallel to the tree to create straight, flat planes and at roughly a 45-degree angle to create curves. Create the desired shape by shearing off the branch tips, but never remove more then 1/3 of the tree foliage as this can cause stress and induce shock.