While some trims can leave shrubs looking thick and shapely, the wrong timing can threaten their health. Both deciduous shrubs and evergreens that maintain their foliage year-round are susceptible to injury when the seasons change -- especially if the seasons cause extreme weather shifts. Bushes also go through seasonal cycles that pruning can easily disrupt. Fortunately, gardeners can safely trim their shrubs by considering the season that is easiest on their plants' health.
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Trimming shrubs at the end of the dormant period -- usually in late winter, between the months of February and April -- is easiest on most shrubs' health. This timing allows bushes to heal from pruning wounds after the worst of winter weather has passed. Pruning also encourages new growths, which appear as spring hits to make shrubs look more robust. If gardeners are worried about trimming away young buds and reducing flowering among spring bloomers, they can wait until midsummer, after the blooming period is over.
Pruning shrubs during the spring blooming period risks removing flowering stems. This also depletes bushes' food supply, which can cause dwarfing, according to horticulturalists Douglas F. Welsh and the late Everett Janne on AgriLife Extension website. Trimming shrubs in autumn is also dangerous as new growths may appear just as the extremes of winter hit, including frozen soil and plunging temperatures; these young growths may not survive the conditions, leaving shrubs straggly in the spring.
Pruning at the wrong time of year will not kill a bush, according to Welsh and Janne, but it does weaken their health, which makes future trims more dangerous as the added stress may make some bushes more susceptible to problems like winter injury and insect infestations. A light pruning that removes no more than 10 per cent of a plant's foliage is usually safe at any time of year, according to horticulturalists on Colorado State University Extension website.
Any shrub experiencing problems -- such as broken branches, insect crazes or disease -- requires immediate pruning before the problems spread to the rest of the plant. In these cases, seasonal timing must give way to promptness. Even broken branches in winter need immediate attention, so the shrub's energy can go to healthy parts of the plant and heal wounds.
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- AgriLife Extension: Follow Proper Pruning Techniques; Douglas F. Welsh, Everett Janne; November 2008
- Virginia Cooperative Extension: A Guide to Successful Pruning, Pruning Shrubs; Susan C. French, Bonnie Lee Appleton; May 1, 2009
- Colorado State University Extension: Pruning Cuts; David Whiting, Robert Cox, Carol O'Meara; July 2009