Dividing Perennial Plants: Why, When, How and What

Division is the most straightforward method of vegetative plant propagation and the technique most often employed by gardeners on a regular basis. The trick is to divide a single plant into two or more plants complete with roots, stems, and leaves. (Pro tip: The leaves can be optional, though it’s good to include some foliage to kickstart growth through photosynthesis.)

When dividing, the right way is to dig and lift the entire plant out of the ground, creating easy access to the roots. However, spreading plants like bugleweed (Ajuga reptans) and turf grasses can be divided by removing clumps without lifting the entire plant. Plants with soft, fleshy roots are excellent candidates for division; they are easily sliced into pieces with a sharp spade. Plants with tougher roots require more serious tools, like hand pruners or a small saw.

Your reward—more plants that you like—is clear, but division benefits the plant, too. In fact, most cultivated ornamental herbaceous plants must be divided now and then to control their size or to rejuvenate their growth: every four to five years for plants like daylily (Hemerocallis), phlox and black-eyed Susan (Rudbeckia hirta); every two to three years for astilbe, lamb’s ears (Stachys byzantina) and coreopsis; and yearly for asters and blanket flower (Gaillardia).

Related: “Signs That a Perennial Plant Needs Dividing”

Of course, there are exceptions. Perennials with taproots, like bleeding heart (Dicentra) and false indigo (Baptisia), don’t like to be divided; they’re best propagated by a different technique.

Also, do not divide weak or stressed plants. Divide only strong, healthy plants.

Successful timing depends on when the plant blooms. It’s best to divide late-flowering plants in early spring and early-flowering plants in late summer. This makes sense. Dividing a spring bloomer, like forget-me-not, a few weeks before it flowers means missing out on its blooms for that season because digging, lifting, and slicing it apart will sap its strength. Better to divide it late in the season so it can emerge the next spring and flower unmolested. Fall bloomers, like ornamental grasses, can be divided in the spring since they will have plenty of time during the growing season to rebound and do their thing.

Related: “When Dividing Plants in Late Summer or Fall, Think Big”

But, again, there are exceptions. Summer bloomers can be divided in spring, so they have time to recover, set buds and flower on schedule, but I have also successfully divided coneflowers in late summer.

Some plants require division when, after several years, their centers die out and they start growing as a ring. Iris and fountain grasses are notorious for this. Hostas and peonies sometimes get so big they need to be diminished to fit their place in the garden. Division does the trick and provides a windfall of clones that can be planted elsewhere or shared with friends and neighbors.

Short-lived perennials must be divided to survive, especially if they have evolved to propagate from seed but their cultivars have been developed with sterile flowers. Examples include shallow-rooted species like yarrow (Achillea millefolium), asters and mums (Dendranthema). Forgetting to lift and divide each spring could be why so many novice gardeners lament the disappearance of their asters after a season or two.

Step 1: Prepare each candidate for division ahead of time by watering as much as a day or at least an hour in advance. This helps hydrate the plant to prevent wilting, loosens the soil for digging and makes it easier to keep the root ball intact as you lift it from the ground. If dividing in late summer, prune any lingering flower stalks or seed heads to prepare the plant for the shock of lifting and dividing.

Step 2: Dig the plant using a long-handled nursery spade. Push into the ground in a complete circle around the plant several inches away from the crown (the area where the stem joins the root) to get the most roots possible. Be patient and loosen the root ball by severing the roots all the way around instead of levering the plant out of the ground.

Step 3: Lift the clump out of the ground while holding the root ball with both hands. Do not yank it out by the shoots! Use hand pruners to clip any stubborn roots clinging to the earth under the root ball. If there are more specimens to dig, place the clump on a square of burlap or a tarp set it in the shade. (Better yet, plan to divide your plants on a cool, cloudy, calm day.)

Step 4: With the clump lying on the ground and your foot on the spade, divide the plant by slicing apart sections of the crown. Divide each clump into two, three, four or more pieces, making sure each division has a healthy chunk of roots and shoots to ensure the new plant’s survival. Use a pruner or saw to cut thick or woody stems and roots.

Step 5: Plant the clones in good garden ground just as you would a new plant from a pot. It’s okay to sprinkle a handful of balanced, organic fertilizer around each plant to kickstart new root growth. Treat them like new plants in every way, keeping them watered and mulched for three to four weeks until they are well established.

Aster (Aster, Eurybia, Symphytrichum)

Bee balm (Monarda didyma)

Black-eyed Susan (Rudbeckia hirta)

Bugbane (Actaea racemosa)

Caladium

Canna

Christmas fern (Polystichum acrostichoides)

Coneflower (Echinacea purpurea)

Daylily (Hemerocallis)

Hosta

Lamb’s ears (Stachys byzantina)

Monkshood (Aconitum)

Ornamental grasses

Rhubarb (Rheum x hybridum)

Tall phlox (Phlox paniculata)

Wild ginger (Asarum)

Windflower (Anemone)

Yarrow (Achillea millefolium)

Astilbe

Bellflower (Campanula)

Bergenia

Coral bells (Heuchera)

Coreopsis

Creeping phlox (Phlox stolonifera)

Dianthus

Gayfeather (Liatris spicata)

Iris

Lady fern (Athyrium filix-femina)

Ligularia

Lily-of-the-valley (Convallaria)

Peony (Paeonia)

Rodgersia

Sedges (Carex)

Solomon’s seal (Polygonatum)