The question of how many peonies to plant together is highly practical for gardeners seeking a lush, abundant bloom. Before considering spacing, it is helpful to clarify the difference between the typical planting material you purchase and a true bulb.
Clarifying Peony Planting Material
Peonies are not grown from true bulbs, which are compact, underground storage organs like those found in tulips or daffodils. The planting material received is actually a tuberous root or a division from an established plant. These divisions must have at least three to five “eyes,” which are the growth buds that will produce the stems and flowers. The eyes must be positioned correctly, typically no more than two inches below the soil surface, for the plant to flower reliably.
Standard Spacing for Herbaceous Peonies
For the most common garden variety, the herbaceous peony, the standard recommendation is to space the divisions approximately three to four feet apart. This measurement is based on the plant’s mature size, which can easily reach a diameter of three feet or more. Peonies are long-lived perennials that can remain in the same spot for decades, so planning for their full, established width is necessary. Giving each plant a dedicated three to four-foot diameter of space ensures they develop into full, rounded specimens. Planting them closer together creates long-term problems as they mature, rather than yielding a dense, immediate hedge.
The Biological Need for Distance
This generous spacing is a fundamental requirement for the plant’s health and successful blooming, not merely an aesthetic suggestion. When peonies are planted too close, they compete with neighboring roots for finite resources like water and soil nutrients, which often leads to decreased vigor and a lower number of blooms. Proper distance is also an effective measure against common fungal diseases, such as Botrytis blight. Crowded foliage restricts air circulation, creating a damp, humid microclimate ideal for fungal spores. Allowing three to four feet between plants ensures air moves freely, helping to dry moisture quickly and significantly reducing the risk of disease development.
Adjusting Density for Different Peony Types
While herbaceous varieties require specific room, the spacing needs of other peony types differ due to their unique growth habits. Tree Peonies are woody shrubs that retain their stems year-round and generally require more space than herbaceous types. Since they grow wider and taller, they should be spaced at least four to five feet apart to accommodate their larger, permanent structure. Intersectional Peonies, also known as Itoh hybrids, are a cross between tree and herbaceous types. These often form a dense, mounded habit and can be planted closer together than tree peonies, with a suggested spacing of two to three feet apart. The key factor in adjusting density for any variety remains its expected mature width.