Columnar apple trees, also known a colonnade apple trees, are upright and narrow fruit bearing trees. In lieu of long horizontal branches, columnar apple cultivars have short limbs that grow at a gentle upward angle from a central trunk. Most cultivars grow to be just 2 feet in spread at maturity and roughly 12 feet high, making harvest and care relatively easy to manage compared to full-size apple trees. The can be grown en masse in an orchard format, as specimen trees or in containers. They require no regular pruning for fruiting but can benefit from light grooming to remove damage or to keep the shape compact.
Remove any damaged, diseased, dead, abrading or otherwise compromised branches throughout the year when you spot them. Cut down to the point of healthy wood or remove the branch entirely down to the trunk, placing the cut just outside the slightly swollen branch collar.
Trim your columnar apple for shape in the summer. Prune back branches that extend beyond the gently tapering columnar form. Cut back the tips of protruding stems, leaving at least three leaves on the branch remaining after each cut.
Reduce the size of your columnar apple tree to keep it compact enough to fit into its location, if needed, by shearing off the branch tips to the desired length. Work around the tree evenly following the natural line of the tree. Never remove more than one-third of the tree foliage and branching to prevent stress and shock from setting in.