Hollies make for excellent hedges, due to their dense foliage and usually evergreen nature. Many different varieties of holly shrub exist, some requiring formal shaping and some only thinning to keep them healthy. Pruning is not only an aesthetic requirement for holly hedges, but it is also a maintenance necessity. Holly hedges can look beautiful all year long if you prune them properly and with the right tools.
Determine what type of holly bushes you have to know what kind of pruning technique you must use. Deciduous hollies, such as Winterberry and Possumhaw, require a radical pruning every year, while rounded hollies like the Japanese holly, Inkberry and Yaupon holly, need thinning during only the first few years of their growth. Blue holly, English holly and Chinese holly ("indeterminate hollies") need thinning and formal shaping throughout their lives. Pyramidal hollies, such as the American holly, don't need formal shaping but do need thinning when young.
Prune your holly hedges in early summer to prevent new growth from being damaged by sudden drops in temperature or frost. Your pruning technique will depend on the type of holly bush you have and the shape you desire, but regardless, always remove dead and diseased branches.
Remove intersecting or crossing branches to a branch union when thinning your holly bushes. Cut parallel to the main branch to hide the stub. Thinning is a simple pruning technique that will simply maintain the natural shape of the holly bushes, as well as reduce overcrowding of branches and improve air circulation in the hedge's interior.
Make cuts at an angle that slopes upward to remove the end of the branches to a bud or leaf node. This formal-shaping technique will give your holly hedges a strong outline. Trim the branches to the desired shape, ensuring that the bottom of the hedge is always slightly wider than the top. This allows sunlight to reach the bottom branches of the holly hedge and prevent the bushes from developing bare legs.
Perform a radical pruning technique if you have deciduous holly bushes. Because deciduous hollies are aggressive growers, you'll need to cut all stems that are thicker than your thumb down to the ground. Remove all branches that are weak, old or spindly, as well as any growth that is extending too far outside the holly bush's main body.