If you want to keep your evergreen tree a particular height, you need to prune it every year or two. When pruning includes the top, it can result in a weakened tree. When the top of an evergreen is cut, it grows multiple new shoots from the cut, causing a fork or prong look. These shoots are weaker than a single main stem, and with weather conditions such as wind and snow, the tree might split at the top. There is, however, a way to prevent this from happening.
Things You'll Need
Sucker growth stopper
Use loppers to snip the top off of the tree where you want the height to be. Cut about 2 inches above a section of limbs, and make the cut at an angle.
Spray a little bit of tree sucker growth deterrent on the cut. This isn't a guarantee, but should help keep new growth from forming out of the cut.
Select a new leader for the top of the tree. Just below where you cut off the top, there should be several stems growing out from the trunk. Pick one to be the new leader, or top, of the tree.
Bend the new leader so that it is pointing up. Bend it as much as you without breaking it, to get it close to the trunk where you made the cut.
Wrap the twine around the main stem below where you made the cut, and then around the new leader. Tie the two together to keep the new leader pointing up so that it will grow in this direction.