Starting the pruning process at planting is advantageous both to the homeowner and the cedar tree. This gives you the opportunity to take smaller cuts from the tree, resulting in less chance of damage or disease. Pruning early on also allows you to shape the tree and remove any branches that might cross each other and eventually leave open wounds on the tree. Pruning should be done only for the health and well-being of the tree and to keep it within a manageable size. Doing this a little each year is safer and healthier for the tree and easier for you.
Prune small branches right after planting your cedar tree. The roots and growth of the tree should be in balance and because planting damages some of the roots, some of the outside growth should be trimmed off. Trim off any branches that are rubbing together and trim the tips off the others.
Prune in the early spring before new growth starts. Cut the 1-year-old tree down to one central leader if more than one emerge. The central leader is the top growth growing straight up. Keep the strongest branch and cut the other(s) off completely to the trunk. This might need to be repeated the following year if a new branch emerges and tries to compete with the central leader.
Prune branches at the trunk each spring to thin out the center so the tree gets sun and good air circulation. Cut to five or six side branches around the tree, leave about of foot of space down and then five or six more side branches. This is known as a whirl. Continue in this manner to the bottom of the tree. Cedars tend to get very thick, which blocks out the sun and causes death to the needles and some branches inside the canopy. Make all cuts at an angle so water flows off the branch and doesn't sit on the cut. This can cause disease to enter the tree.
Prune off all dead, diseased and broken branches any time you find them. Do not leave the debris around the tree but discard it in the trash or burn it to prevent any disease from spreading or pest invasion.
Cut off any bottom branches that are touching the ground. This will allow for better air circulation and prevent the tree from starting new unwanted trees.
Shear the tree once a year in late winter or very early spring. Take off only a couple inches per year to keep the tree manageable. Taking off all the new growth from the year before could result in no new growth or worse, branch death. Shearing can be done with pruners or an electric or gas powered shearer.