When choosing between a thinning and a heading cut, keep in mind the effect you wish to achieve. Thinning cuts result in a more natural look. Heading cuts — and especially shearing — results in a smaller, more geometric, denser look.
In most cases trees and shrubs that need pruning should be thinned. Thinning results in the most natural appearance and in strong growth that is more resistant to storm damage. Plants that are thinned grow at a healthy pace, but remain neater and require less frequent pruning than plants that are headed or sheared. Shearing creates more individual stems, which each produce terminal growth; this, in turn, stimulates more new growth.
Pruning for a Natural Shape
First observe the branching habit of the plant. If the plant has been sheared or improperly pruned, find a specimen that has retained its natural shape. If a shrub forms layers of horizontal branches, try to encourage this type of shape, pruning back the higher branches more than those below to create a tiered effect. For a fountain-shaped shrub of cascading branches, remove older and twiggier branches.
In nature plants gradually self-prune by shedding dead branches at the point of attachment to another branch or trunk. Learn from this example: Prune back to the point of attachment, always leaving a terminal bud on the remaining branch to direct a natural growth pattern.
Pruning for a Formal Shape
Where a more formal appearance is desired, shear shrubs into hedges or geometric shapes. Use heading cuts or shears to create the shape you want. Repeated heading or shearing cuts creates a dense exterior with a multitude of terminal buds. The density of the outer layer, however, blocks light from the interior, which looses its leaves. The shrub will be more attractive if you allow it to grow very slowly, rather than cutting at the same place each time. Allow it to grow from ¼ to ½ inch with each shearing.