Maintenance Pruning
Some shrubs simply require a once a year light maintenance pruning to to keep them healthy and in scale with their surroundings.
Many shrubs can benefit from light pruning beginning at time of planting and then on a once-a-year basis. In general, most shrubs can be pruned while dormant in late Winter, or after they've bloomed in Spring. Keep in mind that dormant pruning of a spring-flowering shrub will remove not just stems, but bloom buds as well.
When pruning a shrub always remove dead, diseased, or broken branches. When pruning dead or diseased branches, make thinning cuts into healthy wood, well below the affected area. Disinfect tools between each cut with products such as "Lysol," "Listerine," or rubbing alcohol. Tests have shown that "Pine-Sol" and household bleach are highly corrosive to metal tools.
In general, to reduce the height of shrubs with a cane habit (Forsythia, nandina etc.), first remove the tallest canes by cutting or sawing them out near ground level. Then, thin out any canes crowding the center, as well as those growing in an unwanted or unruly direction.
For height maintenance of mounding-type deciduous shrubs, prune only the longest branches. Make thinning cuts well inside the shrub mass where they won't be visible. This method reduces mounding shrubs by up to one-third their size without sacrificing their shape.
Large-growing shrubs, with a tree-like habit are the most difficult to shorten. After removing any rubbing branches, prune to open up the center of the shrub. Keep the crown open and maximize light penetration by careful use of thinning cuts. Prune branches that touch the ground and suckers originating from the roots. Wait until the very end of the job to make any heading cuts. Tree-like shrubs can usually tolerate removal of one-eighth to one-fourth of their branches.
Shearing Formal Hedges
Formal hedges are pruned in a totally different way than other shrubs or shrub formations. With only a few exceptions, the proper way to prune a formal hedge is to create a top line that is plumb level, and not necessarily level with the ground below. If the hedge is planted on a slope, it would be appropriate to step the courses down as a series of terraces, with each individual tier still plumb level. On the other hand, informal or natural hedges are almost always pruned to follow the contours of the ground, and are never pruned as rigidly.
To prune a formal hedge to plumb level, hammer in two posts or stakes at each end of the hedge or tier of the hedge, and slightly off to one side. Tie a string taught between the stakes, and then use a line level (a little level which hooks on to the string) to set the string perfectly level to plumb at the desired height of the hedge. Run your pruning tool along the string to remove the top of the hedge along the entire length of the string, being careful not to depress the string in the middle. This task is easiest with a set of power hedge trimmers, but can be done with standard pruning shears as well.
The sides of a formal hedge should also be pruned. In most cases, these are pruned with a gentle slope away from the vertical going down such that the hedge is slightly wider at the base than at the top. This will ensure that the leaves along the side receive adequate sunlight to keep them dense and healthy.
