Peonies - Undeveloped Buds
I transplanted and divided some peonies last year. This year, the foliage looks good but some of the buds are small and black and have never fully developed. What's wrong with them?
Answer: Peonies have few pests or problems. The most frequently occurring pests are botrytis blight and leaf blotch, both fungal diseases. Especially prevalent during wet springs, botrytis affects leaves, stems and flowers. Spots appear on leaves, stems soften and decay, and flowers either rot or buds blacken and fail to open.
Sanitary measures offer the most effective means of control. Start with a thorough cleanup of old, infected stems and leaves and other plant debris in the fall. This reduces the overwintering site for the fungus. Pull the soil away from the crown, without injuring the buds.
In the spring, remove and destroy any wilted or rotted shoots as soon as you detect them. If mulch or another covering is used for winter protection, remove it in the spring before the new shoots emerge from the soil.
Improving air circulation and penetration of sunlight to peony plants often solves the problem. Sometimes, however, chemical control is necessary. If so, spray with a fungicide labeled for botrytis blight, when new shoots appear in the spring. Follow label instructions. Thoroughly soak the surrounding soil. Repeat the procedure a week later and again when the shoots are 3-6 inches tall.
-Beverly Shaw, Purdue Advanced Master Gardener