Add Late-Summer Bloomers
If color in your perennial garden is waning, consider adding some late-blooming perennials, such as aster, rudbeckia, sedum, Joe-Pye weed, Russian sage, and helenium. Blue mist spirea (Caryopteris) is a beautiful, fall-blooming shrub that can be cut back each year to keep it compact.
Allow lawn grass to grow higher to reduce heat stress. Set mower height to 2-1/2 to 3 inches. This also will reduce germination of weed seeds because they will be shaded by grass blades. And be sure to leave clippings so the nutrients they contain will be returned to the soil.
Practice Good Garden Sanitation
Removing diseased plant matter from the garden regularly will go a long way toward reducing problems next year. Dispose of diseased material rather than composting it, unless you're sure your compost pile heats up thoroughly, and you are diligent about turning it regularly to incorporate any partially decomposed material.
Check Soil pH of Acid Lovers
If the foliage on azaleas, gardenias, and other acid-loving shrubs looks pale or yellowish, consider having the soil in the planting bed tested. Your cooperative extension office can provide you with soil test kits. Use sulfur to lower soil pH (make soil more acid).
When using a sprinkler, make sure the water that it's putting out is landing where it's needed -- on lawn and garden areas, not on your driveway, sidewalk, or street. This wastes water and the runoff can pick up and carry oil, fertilizers, pesticides, bacteria, and other pollutants into the watershed. Also, be sure to apply the water at a rate that the soil can absorb to prevent runoff.