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Selecting the appropriate fertilizer for peonies is key to their success. A balanced, slow-release granular fertilizer with an equal ratio of nitrogen, phosphorus, and potassium (such as 10-10-10) is ideal. This type of fertilizer provides a steady supply of nutrients over time, reducing the risk of nutrient burn. Organic options, such as compost or well-rotted manure, can also be beneficial, as they improve soil structure and provide a range of nutrients.