Few perennials can offer what the peony does — beautiful, prolific flowers in early summer and good foliage afterwards. Once established, peonies will flower for many years with minimum care. What’s more, they’re extremely hardy and can easily withstand cold northern winters.
The basic types of peonies are herbaceous (Paeonia officinalis), which grow to heights of two to four feet; fern-leaved (Paeonia tenufolia), with finely dissected leaves; and bush or tree (Paeonia suffruticosa), which may reach four to six feet. The latter produces many flowers on single, shrub-like plants. Then there are the hybrids with flower colors of the tree peonies, yet habit of the herbaceous peonies. These hybrids, and the tree peonies, often are quite expensive.
Most gardeners seem to have better luck growing the herbaceous forms. However, don’t rule out tree peonies if they are hardy in your area. When fully mature and in full bloom, they are spectacular.
Peonies are usually planted in the fall from bare roots, although they may be purchased in the spring or summer as potted plants. They should be planted in an area that receives at least six to eight hours of sun per day. When grown in shady areas, they will produce good foliage but few if any flowers.
The prime prerequisite for good growth and flowering, as with most perennials, is a well-drained soil. You may need to add organic matter, such as coarse sphagnum peat moss, well-rotted manure, or similar material to the soil before planting. Dig it in deeply.
When planting, set the tuber (thickened root) of the herbaceous peony so the buds will be between one and two inches below the surface of the soil. Don’t plant them any deeper because this will produce lots of foliage but few, if any, flowers. The buds or “eyes” on the tubers are bright red, and about one quarter to one half inch long. Generally, herbaceous peonies from bare roots will flower the second year after planting.
Tree peonies are grown from seed or grafts, though most home gardeners have greater success with grafts. It will take at least three years for a grafted peony to flower. When planting the tree peony tubers, dig a hole deep enough to cover the graft with four or five inches of soil. To locate the graft, feel the plant to find the ridging on the stem and the different texture of the bark. By planting deep, the grafted section will establish its own roots in the soil.
After planting any peony, water thoroughly. Mulch with two to three inches of straw, shredded bark, or wood chips kept away from stems. This prevents too much moisture and rots, and prevents the buds of herbaceous types from being too deep.
Next spring, once the plants start to grow and shoots reach three to four inches high, apply a complete, dry fertilizer such as 5-10-10 or 6-10-4 at three to four pounds per 100 square feet of bed area. Or use an organic fertilizer such as 5-3-4 at an equivalent rate, about one-half cup evenly spread around the plant. Water the fertilizer into the soil immediately after application. You also can use high analysis soluble fertilizers, applying them at the rate given on the container. Only one application of fertilizer is generally needed per year to maintain good plant growth and flowering.
Peonies tolerate low fertility, but bloom better with more. Too much, however, and you may end up with all leaves and few flowers. Yearly additions of compost around plants may be all that is needed in fertile soils, and in any soils is beneficial.
If you have an older cultivar (cultivated variety) of peony, you may need to put a peony cage or similar frame around plants in early summer to lessen toppling later. Newer cultivars have been bred to be more upright, sturdy, and seldom need staking.
Keep in mind peonies grow quickly and large early in the season, based on the stored food in the tubers from the previous year. The critical time for this food storage is early to mid summer, so if conditions are dry, make sure plants get plenty of water at this time. This will result in better blooms the following year. When watering, it is best to not water by the stems but in a circumference around the plant canopy.
Providing good air circulation, removing old or diseased flowers, and removing leaves in the fall will help prevent leaf diseases and gray mold on flowers. Ants on flowers do no harm, and are temporary, so should be ignored and left alone. These are merely after nectar on some flowers, and possibly other attractants. They may even help open tight double buds on some.
Peonies are easy to propagate, though usually they do not need to be divided for 10 to 15 years or more. Divide by digging up the plant in fall and separating the tubers, making sure each has three to five buds. Remove any damaged tubers or those with signs of disease. Plant the good tubers as described above.
Dr. Leonard Perry is Extension Professor, Department of Plant and Soil Science at the University of Vermont. Visit his website at http://www.uvm.edu/~pass/perry/index.html