[header] How to trim shrubs [title] Examine your shrub for blooms to determine when you should trim it. [step] For blooming shrubs, trim them in the winter when they're dormant to prevent stunting flower growth. You can trim non-flowering shrubs anytime except late autumn when any new growth the plant has after trimming won't have time to mature before it goes dormant. 
[substeps] If you're growing a hedge, trim it when the branches look overgrown until about 6 weeks before your area's usual first frost. Avoid doing extensive trimming when it is not your shrub's trimming season.