white birch trees and
red maple min. trees?
|Peonies should be allowed to grow untouched until frost kills the tops of the plants. At that time you can cut all the dead foliage down to ground level. It's okay to cut off the flowers and their stems when the flowers are spent or if you'd like to take them indoors for a fresh flower display, but the rest of the foliage should be left alone until it dies back after your first frost in the fall.
Forsythia blooms in late winter/early spring and can be pruned back after it has finished flowering. The growth it puts out over the summer months is what will provide next year's flowering so if you prune too late in the summer, you won't have quite as much new growth and you'll see fewer flowers next winter/spring.
Birch trees should be pruned in late winter or early spring. If you prune in the summertime when bronze birch borers are active, the new pruning cuts can attract these pests. So prune when they are not active and your birch trees will have the potential to remain healthy without the threat of an insect invasion.
Maple trees are pruned in the winter when they are dormant, or in the early spring just as new growth begins.
Best wishes with your landscape.