Pruning Overgrown Shrubs
I recently purchased an older home with large, overgrown shrubs. They block windows and grow over the lawn and sidewalks. They have been sheared with flat tops which I hate. Is it possible to drastically reduce them in size without ruining them?. Can I prune now or should I wait until fall or spring?
If you prune too late in the summer, new growth may not have time to harden up before winter cold, making it more susceptible to winter damage. As a general rule I prefer not to do heavy pruning past mid-September. Fall pruning can begin about mid-November.
The main pruning cut needed to return sheared shrubs to a natural shape is thinning. This means removing about 1/3 of the branches deep inside the shrub. Plants which have been sheared several times will have clusters of 3 or more branches growing out from the same point. Deeper in the plant, you will probably find another cluster. Prune below the first and second clusters if possible. With one cut, you will be removing 3 to 12 branches or branchlets. Remaining branches can be pruned by about half as much. I like to start at the bottom of the shrub and gradually prune branches shorter as I move up. This gives a rounded or curved natural shape.
If you prune evergreen shrubs back into the brown area with no green leaves remaining they will never produce new green growth. If they need to be reduced in size that much, they should be removed and replaced. Some flowering shrubs which have become overgrown can be drastically pruned back to within a few inches of the ground. They will grow new branches which can be pruned to retain a natural shape. Rhododendron, Pieris, Forsythia, Ceanothus, Escallonia, Euonymus, Hydrangea, Nandina, Viburnum, Barberry, Potentilla, Red Twig Dogwood, Spiraea and Lilac will all respond to this type of pruning. Remember, however, that you are sacrificing a year’s flowering when you do this.
Where branches are growing out over the lawn consider moving the lawn back so you have a wider bed for the shrubs. This will leave more room for shrub growth with less drastic pruning. Where shrubs are growing over a walkway or blocking windows, your best choice may be to remove them and plant shrubs which grow smaller.
Allen Wilson
Allen has been writing about gardening for over 30 years. He is a retired professor of Horticulture.