A Bay Weekly reader lamented over how tall her azaleas had grown. She could no longer see out of the living room windows and would have to pay to have them replaced. I told her that all she had to do was cut them back to at least two inches below the ledge of the window. The plants would rejuvenate. The expression on her face clearly indicated that she thought me a complete idiot.
Plants are survivors. If you know which species can be rejuvenated and which cannot, you can save much time and money. Azaleas, rhododendrons, mountain laurel, cherry laurel, lilacs, privet, hollies, pyracantha, roses, forsythia, weigela, viburnums, yews and buddleia can be pruned back to individual stems that will renew branches.
How to Prune Boxwood
Many years ago, I planted English and American boxwood together in a hedge. The American box is now twice as tall as the English. Can the American box be cut in half and trimmed without killing it?
Boxwood can be pruned very severely in early spring and will bounce back with lots of sprouts along the stem. However, I encourage you to sterilize your pruning tools with alcohol. Boxwood blight has been reported in Maryland, and the disease is spread by pruning tools as well as by insects. I am advising boxwood owners to prune boxwoods like the English do, by reaching into the plant and snapping the branches. Boxwood wood is very brittle and the branches break easily providing they are less than half an inch in diameter.
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Prune these species severely in early spring, before new growth begins.
These species can tolerate severe pruning because they have a high population of latent vegetative buds hiding beneath the bark. Vegetative buds occur naturally in the axils of most of the leaves that are produced in each stem. In general, only vegetative buds near the ends of a stem generate new branches. The remaining buds remain dormant and are activated only when something happens such as pruning, freeze damage or some accident.
When you prune severely in early spring, the large root system forces the latent buds into active growth. If you prune a large azalea severely to only single stems, you will notice a profusion of new growth along the stems by early June. By mid to late June, you will need to thin the branches to allow a minimum of two to four inches of space between them. If you don’t thin or space the branches, the population of branches will be too dense and you will likely see some dying from excessive competition.
However, such species as arborvitae, junipers, chamaecyparis, spruce, Leland cypress, pine and fir will die if you prune the plants down to single stems with no needles attached. These species develop vegetative buds only in the clusters of needles or adjacent to needles near the ends of branches. Prune these plants severely, and they will not recover. Leave no visible needles and the plant dies.