Thuja occidentalis is a member of the arborvitae genus, a group of evergreens that are known for being easy to care for and maintain. Thuja occidentalis grows quickly, however, and will reach 12 feet in height when mature. It is best to prune Thuja twice annually to keep it down to a manageable size and desirable shape. If at all possible, don't miss any appointments. It may take several seasons for Thuja to recover from the hard pruning necessary to cut it back down to size.
Pinch 2 inches off the tips of the newly grown (they will be a lighter green than the older foliage) stems of a young Thuja during its first two seasons of growth in your yard. This will encourage new stems to branch out and fill out the interior.
Remove any branches of your Thuja that sport brown needles. These branches are dead and must be cut back to their point of origin. Use a pair of sharp lopping pruning shears to cut the branch back to its collar, the swollen point at the base of the branch.
Shear your Thuja hedge to create a desirable shape. Use hedge clippers to trim away the overgrown new growth (a lighter green than the older growth) on the top and sides of the hedge until it resumes the shape you want. When pruning, keep the top of the Thuja slightly narrower than the bottom to prevent the upper branches from blocking the lower branches' access to sunlight.