One may have plants that have yet to reach maturity or, and this is probably the most common reason, the paeonies were planted too deeply. Other contributing factors may include too much nitrogen, too old a clump or the plants have been moved and divided too often. On other occasions, buds form but fails to open. The new buds are susceptible to late killing frosts. Excessive rain or excessively hot weather can also contribute to non opening of flower buds.
Paeonies are gross feeders and a lack of nutrients can also lead to buds failing to open.
For the most part paeonies are trouble-free plants. Most problems are caused by fungi. Botrytis paeonia and Botrytis cinerea are both important pests. They are more prevalent in North America and China, respectively. The former causes 'Botrytis Bud Blight'.