If you haven't already, prune your roses now and feed them with a fertilizer made for roses. Begin spraying them for black spot. Following the directions on the package.
Prune your shrubs this month if you haven't already. Don't prune any spring flowering shrubs as you will cut off their blooms. Wait until after they have finished blooming to prune them.
Divide and transplant late and summer blooming perennials. Wait until fall to divide any early bloomers. Check the "How to divide Perennials" for a list of perennials you can dig up and divide now if you have any doubts.
Remember to leave the foliage on your spring blooming bulbs to die back naturally. Your bulbs get their energy for next year's blooms for the foliage. You can gather up the dying leaves and tie them in a bunch or just plant other flowers to grow and hide them as they are dying back.
You should cut back your grasses now to about 2 - 3 inches, such as liriope, pampas grass and mondo grass.
Fertilize your trees and shrubs if you didn't do it last month.