1. Insufficient Sunlight
Peonies are sun-loving plants, and one of the top reasons their buds fail to open is a lack of sufficient light. These flowers require at least six to eight hours of direct sunlight daily to encourage healthy, vigorous blooming. Without enough light, the buds may form but remain closed because the plant lacks the energy it needs to fully develop the flowers.
Solution: If your peonies are in a location with too much shade, consider transplanting them to a sunnier spot in early fall. Alternatively, trim any overhanging branches or foliage from nearby trees or shrubs that may be blocking the sunlight.

2. Watering Issues
Improper watering, either too much or too little, can stress peony plants and cause buds to hold back. Overwatering can drown the roots, while underwatering may dehydrate the plant, preventing the buds from maturing.
Solution: Peonies prefer well-draining soil and consistent moisture, especially during the growing and blooming season. Water deeply once or twice a week (depending on weather conditions) and make sure the soil dries slightly between waterings. Mulching around the base of the plant can help maintain soil moisture while preventing root rot.

3. Pests or Fungal Diseases
Pest infestations or fungal issues can also interfere with a peony’s ability to bloom. Aphids are notorious for targeting peony buds, feeding on them and causing distortion that prevents proper opening. Similarly, gray mold (Botrytis blight) can attack buds, making them brown, shriveled, or covered in fuzzy mold before they even get the chance to open.
Solution: Regularly inspect your peonies for pests like aphids. If you notice an infestation, spray the plants with a strong jet of water to dislodge the bugs or use insecticidal soap to control the population. To prevent or address fungal infections, ensure proper airflow by spacing plants apart adequately and removing any infected parts immediately. A fungicide can be applied as needed.

4. Nutrient Deficiency
Peonies are not heavy feeders, but they do need a reasonable amount of nutrients to support bud development and blooming. A lack of phosphorus, in particular, can hinder flower production. If the soil is poor in nutrients or overly packed with nitrogen (which promotes leafy growth rather than flowers), your peony buds may struggle to open.
Solution: Test your soil to determine if it is deficient in nutrients. If needed, add a balanced fertilizer (e.g., 10-10-10) or one with higher phosphorus content. Apply the fertilizer sparingly and only in early spring or after the blooming season to avoid overfeeding.

5. Planting Depth Problems
Proper planting depth is critical for peonies. If the tuberous roots are planted too deeply, the buds may form but fail to open because they cannot receive the necessary cues from the environment.
Solution: Check the crown of your peony plant to make sure it is at the correct depth. Ideally, the "eyes" (growth buds) should be 1 to 2 inches below the soil surface. If the plant is buried too deeply, consider carefully digging it up and replanting it at the right depth in early fall.

6. Temperature Fluctuations
Peonies are hardy, but sudden changes in temperature during spring can stress them. Early warmth followed by a cold spell or late frost may damage the buds, causing them to remain closed or drop off altogether.
Solution: To protect peony buds from late frosts, cover the plants with a light fabric or frost blanket when cold weather is forecast. Avoid planting peonies in areas that are prone to extreme temperature swings, such as near heat-reflective walls or in low-lying areas susceptible to frost.

7. Aging or Crowded Plants
Older peony plants that have been in the same spot for many years can become overcrowded or depleted, which can result in fewer blooms. Similarly, if the plant has not been divided in a decade or more, it may struggle with bud development.
Solution: Dividing peonies every 8 to 10 years can rejuvenate the plant and improve blooming. This process should be done in early fall. Carefully dig up the peony, divide the root clumps into smaller pieces (each with 3-5 eyes), and replant them in well-prepared soil.

Mist the Buds: Sometimes, buds are simply too dry to open. Use a fine misting spray bottle to gently moisten the buds, softening the outer layers and encouraging them to unfurl.
Support the Plant: Staking tall stems or using peony rings can reduce stress on the plant and help the buds focus on maturing rather than balancing heavy blooms.
Pinch Off Smaller Buds: If your peony plant has multiple buds on one stem, removing the smaller secondary buds can redirect energy to the main one, making it more likely to open fully.