Pruning a buckthorn helps to keep the shape of the plant and it encourages new growth. The pruning process needs to be performed during the buckthorn's dormant stage to prevent injury. During regular pruning, you will need to remove diseased and damaged branches to keep the buckthorn healthy. The buckthorn can become invasive in wetlands due to its dense growth, in which the whole plant often needs to be removed to allow other species to grow.
Prune the buckthorn during the late fall or the early spring. Typically, it is easiest to prune the buckthorn tree after the winter season. You need to wait for the tree to become dormant, but if you live in a warm climate, you will need to prune in the early spring to help encourage the plant to grow.
Remove dead and decayed wood from the buckthorn. Use garden shears to reduce shredding of the buckthorn. Cut the plant to the desired shape. In order to maintain the shape of a columnar buckthorn, you will need to prune 1/3 of the oldest branches at the base by selecting random branches and spreading them out evenly.
Prune the buckthorn throughout the year. You will only want to prune the buckthorn to maintain its size and shape, but you will cut less of the plant throughout the year. Cut off branches that interfere with your landscape or that need to be maintained.
Remove the clippings from the ground. This can grow mold and cause disease. Add them to a compost pile.