Green with Reene
When should you cut back trees, shrubs and flowers? You can trim trees anytime. Cut back to the branch collar and be sure to make a clean cut. Do not paint the wound, allow nature to heal on its own. Trim shrubs back when they have finished their blooming season. They will not bloom for you if you cut them before their blooming time.
With shrubs use the 1/3 method—trim the entire bush one-third all the way to the ground, the second year take back a third again, and do it once more the third year. Take out the oldest wood stems as you go. Trimming this way allows your shrub to keep a natural look and in three years you will have a new bush. You need to deadhead flowers, both perennials and annuals, as soon as they are done blooming—lots of them will bloom again. Deadheading will allow more bloom, allow you to control reseeding—if you want that control, and it will allow the growth to go into the plant. They will also look a lot better.
If you like gardening, I recommend the Master Gardener course offered at the Extension Center of your State University. It is a wonderful way to learn and to give back to your community.