Q. I’m having trouble with my tall phlox plants. They are covered with white powder each summer and are smaller than they used to be. The flowers are fewer and smaller, too. Should I spray them with something? &emdash; Jane Small, Fort Wayne, Ind.
A. Several factors contribute to vigorous blooming of old-fashioned phlox (Phlox paniculata). The white powder is powdery mildew, and phlox and lilacs are especially susceptible to this fungus. Appropriate fungicides will help but require repeated applications during the growing season and year after year. Since full sunlight and good circulation reduce the severity of powdery mildew, the wisest choice is to move the phlox to a sunny site and give it plenty of space. Full sun and deadheading (removing spent blossoms) will encourage flower production. Divide the plants every three to four years in the spring or fall to maintain vigor.
Q. Our mums grow 28-36 inches tall and after they bloom, they fall over. How can we keep them short, like they were the year we bought them? Why do so many die each winter? It seems like we lose half of them every year. &emdash; Marian Sipes, Otterbein, Ind.
A. Chrysanthemum growers use chemical sprays to increase branching and to dwarf the plants, so the plants are short in the garden center but will be taller the next year in your yard. To have shorter, well-branched plants, remove the growing points once or twice during early growth. Pinch them back when the plants are about 6 inches tall (about mid-June) to induce branching. When the branches are 6-8 inches long (about mid-July), remove their tips to induce more branching. This procedure may seem drastic, but the results will be bushy, well-shaped plants that flower abundantly. Many old garden sayings have a grain of truth to them. The axiom “Pinch mums until the fourth of July” may help you remember how to care for your mums.