I live near Philadelphia, Pa. and have a False Spirea that blooms in August. When can I start to prune it and trim it back; it’s starting to get overgrown?.
False Spirea (Sorbaria sorbifolia) is a deciduous shrub shrub that blooms on new wood. In the Toronto area this shrub usually blooms in June.
This is a very good shrub for shady areas but it does have a suckering nature which, if not controlled, will take over a large area, particularly if the soil is nice and lose.
Generally, you prune this shrub hard in early spring just before the buds start to break. Then prune for shape again after it blooms.