Perennial peonies grow in shades of black, white, red, pink, purple and yellow, blooming for 6 to 8 weeks. The plants have rich green foliage in normal conditions. For healthy peonies, plant them in full sunlight in a protected site, with well-drained soil that has a pH of 6.0 to 7.0. Not all peonies, however, stay healthy even under good conditions. When white leaves occur on peonies, it’s because the plants are unhealthy in some way.
Powdery mildew may create a white film on peony leaves. The flowers may seem unaffected by the mildew, but it will weaken the plant and make the foliage look white and unhealthy. Powdery mildew won’t kill peonies, but will make the plant unattractive. Cut or pick all the affected leaves to prevent powdery mildew from spreading. If this doesn’t resolve the problem, apply fungicide that will kill mildew on plants without causing damage to the plants.
White mold creates wilting of the stem, which affects the entire plant and may kill peonies. Infected stems will look light tan. In humid weather, fluffy white specks may appear on the plant. White mold will appear as hard, black spots inside infected peony stems. Cut the stem open lengthwise to look for the spots. All infected plants must be removed from the garden, roots and all, to keep other plants healthy.
Improperly planted peonies are more prone to be affected by disease. Keep peonies in well-drained soil and plant them in a site where they’ll receive wind protection and normal air circulation. Cut away all diseased plants in the fall and dispose of them properly–don’t place them in your compost pile, but burn them or throw them in the garbage. Apply a 2- to 3-inch layer of mulch around peony plants to help the soil retain moisture and prevent the growth of weeds. Properly planted peonies will resist diseases that cause white, unattractive leaves.