Routine Peony Feeding
Phosphorus and nitrogen are important nutrients for a peony over its lifetime. You must ensure proper levels each year so that your plants will grow as they should and produce vivid blooms. Apply a low-nitrogen fertilizer — a 5-10-10 blend, for instance — to the soil around the peony stem. This should also help keep phosphorus levels steady, but test your soil every few years to make sure you’re feeding your peonies correctly. Adding bone meal or phosphate fertilizer occasionally assists in strong root growth and flower set.
Peonies require fertilization in the spring after growth has begun and stems are roughly 2 to 3 inches high. If the peonies in your garden or yard are well established, consider waiting to feed them until the flower buds are pea size; fertilizing older plants at this time contributes to healthy flowering. Dividing and replanting peonies occurs in the fall, so you may need to adhere to special fertilization needs at that time, such as amending soil with well-rotted compost to boost nutrient content or scattering a handful of bone meal around the newly divided and replanted peonies to encourage strong root development.