Answer: Pruning woody perennials can be done after they have finished flowering. For spring flowering shrubs, wait until the flowers are spent; for summer flowering shrubs such as lavender, you can prune in early spring or you can wait until after they have finished flowering in late summer. Mums can be deadheaded when the flowers are spent or you can wait until early spring to cut everything down - new flowering shoots will develop from the roots. Hope this clarifies things for you.
As for deadheading roses, most rosarians believe that leaving the last of the flowers on the plants and allowing them to become rosehips signals the plants to stop developing flowers and to go into a resting phase. I tend to agree with the experts. Besides, the rosehips look attractive in the winter months. In your climate, roses seem to want to grow year around. This can cause diseases such as blackspot to hang around from one year to the next. One way to control this problem is to remove all of the foliage and rosehips in December (just pick them off one by one). Then do your pruning in January when new shoots appear.
Best wishes with your garden!
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