Revitalize Repeat-Blooming Daylilies
Prune away dead daylily stems. Fertilize rebloomers, such as 'Happy Returns', 'Stella D'Oro', 'Rosy Returns', and 'Red Hot Returns' with slow-release fertilizer higher in phosphorus and potash than in nitrogen. Apply fertilizer to moist soil. Repeat-bloom varieties will rest after blooming for two or three weeks, then can rebloom till frost if well fed and watered. When buying, look for the word "rebloomer" or "returns" on the label. These are usually smaller, more compact plants than the once-bloomers.
Shear Dead Leaves on Once-Blooming Daylilies
When the foliage turns brown and unsightly on daylilies that bloom only once, cut or shear off the dying leaves. Feed with a slow-release fertilizer higher in phosphorus and potash than nitrogen (for next season's flowers). The foliage will regrow to look lush and green in several weeks. It's also okay to divide daylilies anytime after flowering. Dividing crowded clumps may revitalize their bloom next season.
Cut Back and Deadhead Perennials
Cut back delphinium flower stalks and phlox after they flower to encourage more flowers in the fall. Clip directly below the dead flower heads. New buds form lower on the stalks.
Deadhead daisies, dianthus, echinacea, monarda, and corepsis. Removing dead flowers on these plants encourages further flowering. Clip flower stalk near the base, above the basil foliage at ground level.
Cut back leggy begonias now for more flowers in September and October. Water annuals regularly, and apply fertilizer to moist soil (to avoid fertilizer burn). Annuals need about an inch of water a week from rain or irrigation. So water at least once weekly, soaking the soil to a depth of 6 to 8 inches.
Treat Powdery Mildew
This summer's rain, humidity, and high temperatures are ideal conditions for powdery mildew, a gray-white powdery mat on leaves, stems, and flower petals. Powdery mildew is the name given to a group of diseases caused by several closely related fungi. Untreated, the mildew will spread via airborne spores and infested plant material. Repeatedly applying fungicide is an option. My preference is prevention where possible and removing infested foliage, stems, etc. When necessary, I use less toxic products, such as Neem or Serenade. There are new products with potassium bicarbonate (related to baking soda) that I haven't tried. Be sure to spray from the top and bottom to cover stems and entire leaves.