Prune blue spruce trees in spring by removing fresh growth from the tips. It is not necessary to prune blue spruce trees, but it does promote denser foliage.
To prune a blue spruce tree, start by removing all the dead branches. Cut dying branches back to the branch collar, which is the thickened node that connects the branch to the trunk. Both of these actions can be completed at any time with no harm to the tree, though trimming during dormant time minimizes sap and resin flow.
If it is necessary to prune the blue spruce more significantly because of height or width restrictions, cut branches that show little needle growth. Cut the branches using the three-cut method. Come 12 inches out from the trunk and cut halfway through the branch from the bottom. Then, move out an additional 2 inches and cut down from the top, then remove the branch. Make the final cut near the branch collar, being careful not to injure it.
Cut other branches to shape the tree or promote dense foliage. The central leader, or trunk, should not be pruned as new leaders may grow in weak, making them prone to damage from snow and wind. Side branches should be under half of the diameter of the trunk to maintain the structural integrity of the tree.