Fern leaf peonies (Paeonia tenuifolia) are unique among peonies because of their fern-like foliage. When the plant first emerges in spring, it resembles an old-fashioned shaving brush. It is interesting to watch as it gradually opens out into a light and airy mound of foliage that stands about 18 to 24 inches tall. The 2 1/2- to 3-inch, bright red flowers that bloom in late summer have very short stems and they appear to sit directly on the foliage. Fern leaf peonies are hardy in U.S. Department of Agriculture plant hardiness zones 2 through 9.
Sun and Soil
Fern leaf peonies need full sun and moderately moist but well-drained soil. The tubers rot in soil that is constantly wet or soggy. While fern leaf peonies will grow in most types of soil, they prefer soil with plenty of organic matter. They establish slowly but bloom well in clay soil. In sandy soil they produce more foliage and fewer flowers. Working plenty of compost or rotted manure into the soil helps get them off to a good start.
Water and Fertilizer
Water fern leaf peonies often enough to keep the soil moderately moist. In areas with hot or dry summers this may mean deep weekly waterings. Feed fern leaf peonies with a mixture of bonemeal and either compost or well-rotted manure in the fall before the foliage fades. If you prefer to use a commercial fertilizer, choose one with a lower percentage of nitrogen than phosphorous and potassium. High levels of nitrogen lead to fewer flowers.
Fern leaf peonies are herbaceous plants that fade into the ground in the fall and emerge again in the spring. They emerge a little later than other peonies, so it's a good idea to mark their location so that you don't damage the tubers or crowd the plants when you begin working the garden in the spring. Organic mulch helps maintain soil moisture and reduces the number of weeds. Removing the flowers as they fade encourages more blooms. Wait until fall frosts begin to kill the foliage before trimming back the stems for winter. Then cut the stems off just above the crown.
Fern leaf peonies sometimes die back in midsummer the first year or two after you plant them. This is normal in areas with hot summer temperatures and is not a cause for concern. You can hide the hole left in the garden bed by planting summer annuals in the area between the dormant plants. Dig carefully so that you don't disturb the tubers.
- Iowa State University Extension: Fernleaf Peony is a Precious Gem in the Garden
- Perennials.com: Paeonia Tenuifolia
- The Gardener's Guide to Growing Peonies; Martin Page