Carefully Remove Rhodie Seed Heads
If not done yet, now's the time to remove seed clusters that formed after spring flowering on rhododendrons. Each seed head sits atop emerging buds so this is tricky. Hold each seed cluster at its base with finger and thumb. The seed capsules on brown stems should be in your hand. Twist and pull so the cluster comes off with a snap of the wrist. The American Rhododendron Society recommends this to prevent heavy seed set, enhance the shrub's beauty, and reduce the prevalence of fungus.
Deadhead To Stimulate New Flowers
Pruning to remove dead flower heads from salvia, veronica, lady's mantle, malva, coreopsis, valerian, and perennial geraniums can make way for continued or later flowering. For lady's mantle, coreopsis, and geraniums, individually cut off each dead flower stalk at the base of the stalk. Clip salvia, valerian, and veronica more carefully -- just below the dead flower head. Look carefully and you'll see small flower buds emerging lower on the same stalk.
Shear to Tidy Up and Encourage More Blooms
Dianthus, candytuft, and creeping phlox may (or may not) rebloom later in the season. Clipping away dead flowers increases the possibility. For large swaths, I shape and prune foliage and flower stalks with sharp, long-bladed, hedge or grass shears, removing 2 to 3 inches. Shearing rangy catmint early will keep plants looking compact and promote rebloom.
Cut Off Spent Flower Stalks
Iris, poppies, hellebores, columbines, brunnera, and heuchera won't rebloom this year. As sculptural accent (and for reseeding), it's fine to leave a few attractive poppy, iris, and columbine seed heads for texture and height in a summer garden. Otherwise remove dead flowers by clipping off each flower stalk at its base.
Remove Dead Leaves
Removing dead leaves makes room for new foliage. This improves the plant's health and the garden's overall appearance. Look at the leaves carefully, top and bottom, for insect or disease damage. Dead leaves may be natural or a symptom of a larger problem. If there are spots, chewed edges, moving critters, or other suspicious signs, take a fresh sample to your local Extension Service office, arboretum plant clinic, or garden center to get help identifying the problem.