Reduce the size of overgrown shrubs
Question: In your recent column about overgrown shrubs why didn’t you address the man’s question? He was asking if he could restore the shape of topiary, not asking about replacing shrubs.
Answer: I did not see “topiary” in his question. However you are correct. I will try to address both his real question and yours now.
The reason my emphasis was on replacing shrubs was because that is usually the only practical solution to the type of problem he describes: “The shrubs have been sheared so they are all round balls or boxy hedges. Some have lost their leaves at the bottom and look top heavy. Is there any way to restore the natural shape of these shrubs.”
I can see how you interpreted this as topiary which trains trees and shrubs in a series of balls or other artificial shapes. One common type is referred to as a “poodle cut”. If you have shrubs which have been trained in shape and have become overgrown, you can definitely try to restore them to their trained shape.
Topiary plants need regular pruning, at least once a year. As new outer growth develops it shades the inner growth which then loses its leaves. If cut back to their original shape, overgrown plants may have spots with no leaves or only brown twigs. Needle leaf evergreen shrubs seldom regenerate new growth from this brown tissue. Try not to cut beyond the point where there are green leaves or needles.
I recently converted a spiral cut Alberta Spruce back to a simpler pyramidal form. I simply did not prune the branches in the spiral grooves. These branches and the ones next to them will soon grow over and cover the grooves.
Drastically reducing the size of overgrown shrubs (more than 1/3) will often result in exposing branches with no leaves. Most needle evergreen plants will never regenerate green tissue from these brown areas. If the areas are small, new green tissue may grow over from adjoining areas.
On the other hand broad leaf evergreen and deciduous shrubs will usually regenerate new growth even when cut back to within a few inches of the ground. Shrubs such as rhododendron, andromeda, pyracantha, Oregon grape, nandina, spiraea, potentilla, willow, lilac, barberry, forsythia, euonymus and privet will all respond to drastic cut backs. You can prune those way back now or after they are through blooming. You will need to do a little pruning this summer to even out irregular growth. Then continue to prune each year so that branches do not grow beyond the size you want them. Prune one branch at a time and do not shorten them to all to the same length so they will look more natural.