When to Divide Peonies & Day Lilies

Peonies (Paeonia spp.) and day lilies (Hemerocallis spp.) bring two desirable elements for the perennial garden -- lots of blooms and distinctive foliage from spring through fall. Both require little except for plenty of sun, well-draining soil and moderate moisture. Divide both periodically to make new plants, either to use for landscaping or to expand the garden. Divide peonies in fall and day lilies in early spring or in fall.

Garden peonies (Paeonia lactifolia), which grow in U.S. Department of Agriculture plant hardiness zones 3 through 8, tree peonies (Paeonia suffruticosa) and fernleaf peonies (Paeonia tenuifolia), which grow in USDA zones 4 through 8 and Japanese peonies (Paeonia japonica), which grow in USDA zones 5 through 8, all need root growth and winter chilling to produce blooms for Memorial Day.

Day lilies, whether old tawny day lilies (Hemerocallis fulva), which grow in USDA zones 3 through 9, lemon day lilies (Hemerocallis lilioasphodelus), which grow in USDA zones 4 to 10 or their many descendants and cultivars, root readily almost any time of year but in the heat of summer.

Some plants live decades, so give your garden peonies five to 10 years to build a good stand before you divide them to make more plants. Dig holes 12 inches deep and wide before dividing peonies in September in USDA zones 3 through 5 -- plants can be lifted in early October in higher zones. Lift the entire plant with a garden fork.

Trim the stems to 1 inch above ground level with shears. Shake off as much soil as possible and dip the tuber in a bucket of lukewarm water or clean it with a soft brush. Use a sharp knife to cut the tuber into sections containing three to five eyes -- the little buds that form where next year's stems will grow. Discard spongy parts of the tuber or sections with worm holes. Set the eyes no deeper than 1 to 2 inches below the surface in the prepared holes. Fill, water well and mulch with a 3-inch layer of pine straw for the winter.

Divide day lilies every three to five years. Split and lift clumps with a garden fork in early spring after the soil has warmed or after flowers fade in August through early October. Pull the clumps can apart by hand or divide with a sharp, sterile knife. Establish clumps of three to five fans and trim off any broken roots. When dividing plants in fall, trim fans back to 4 inches. Make small mounds of dirt in each hole and spread roots over these mounds, keeping the crown -- the white fleshy base of the plant -- within 1 inch of the surface as you fill the hole. Water well and spread a 2- to 3-inch layer of mulch to conserve moisture.

Choose spots for new plants where they receive six to eight hours of sun each day. Add well-rotted manure or compost to improve soil tilth. Wipe all tools used to cut plants with a cloth soaked in rubbing alcohol between plants to prevent plant disease.