Pruning is as much an art as a science. That is, there are guidelines but you have a lot of leeway in how you go about it and how you want the plants to look. Some folks like a sheared, formal look while others prefer a more natural look. Shrubs vary in their response to such approaches. The plants you mentioned are flexible with either approach. Shearing is done from spring to late summer or early fall. You can usually get by with shearing every 4 weeks depending on the type of shrub and its growth rate. Less formal pruning is done periodically to remove gangly shoots and to shape the bush a little without shearing it. The following web sites offer a little more info on pruning various types of shrubs.
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