How to Divide Perennials Without Killing Them

The Short Version

To divide a perennial, do it in spring or fall while the plant is not blooming. Water a day or two ahead, cut the top growth back to about 6 inches, lift the whole clump, split it into pieces with three to five shoots each, and replant them at the same depth. Water them in well. For a fall division, leave four to six weeks before the ground freezes so the roots can settle.

The extension guides warn against three avoidable mistakes: dividing in bloom, dividing on a hot sunny day, and letting the divisions dry out before replanting. The rest of this guide covers timing, the method, and which plants to split or leave.

How to Tell a Perennial Needs Dividing

A clump grows outward from its center, and the oldest growth in the middle weakens over time. Clemson’s fact sheet lists the signs: flowers that are smaller than normal, centers of the clumps that are hollow and dead, and bottom foliage that is sparse and poor. Oregon State University Extension describes the same picture as a dead center, thinning growth or fewer blooms. Penn State adds a fourth reason, a robust perennial that is beginning to crowd out its neighbors.

If the plant is vigorous and flowering well, leave it. The intervals later in this guide are averages, and the plant’s condition overrides them. A drop in bloom alone can have other causes, and deadheading for more blooms is worth trying first on a young clump.

When to Divide: Spring or Fall, Never in Bloom

Penn State Extension’s rule is the simplest: divide when the plant is not in bloom, so it can put its energy into root and leaf growth, with spring and autumn as the recommended times. Oregon State puts it more bluntly: “Never divide a plant while it is blooming.”

Extension sources then split slightly on which season suits which plant, so here is what each one says:

• Oregon State: divide summer and fall bloomers in spring, and spring bloomers after flowering or in fall.
• Clemson (South Carolina): divide spring and summer bloomers in fall, and fall bloomers in spring.

Both agree on the two ends. Fall bloomers such as asters and chrysanthemums go in spring, and spring bloomers go in fall. Summer bloomers can go either way, and your winter decides. Penn State notes that where spring is late and short, September division is preferable, allowing four to six weeks for the plant to establish before the ground freezes. Clemson gives the same four to six weeks and, for South Carolina, a fall window from early September in the uppermost Piedmont to mid or late October on the coast.

Pick the day as well as the season. Clemson advises never dividing on hot, sunny days and waiting for a cloudy day, ideally with several days of light rain in the forecast. If autumn is your season, the guide to dividing perennials in fall goes plant by plant through the fall window.

How to Divide a Perennial, Step by Step

You need a spading fork or sharp spade, a knife, and for big clumps a second fork. Clean, sharp pruning shears handle the cutting back.

1. Water first. Water the plant thoroughly a day or two before dividing if the soil is dry.
2. Cut back the top. Trim stems and foliage to about 6 inches from the ground. This makes the clump easier to handle and to see.
3. Lift the whole clump. Dig around the plant with a fork or spade and pry it up in one piece.
4. Split it. Pull small or fibrous-rooted plants apart by hand or cut them with a knife. For large, dense clumps, push two forks into the crown back to back and lever them apart. Tough, woody crowns need a sharp spade or a saw.
5. Size the pieces. Aim for divisions with three to five vigorous shoots each. Discard the dead center and keep the younger outer sections.
6. Keep roots moist. Clemson suggests keeping a pail of water nearby to moisten divisions until they are planted.
7. Replant at the same depth. Set each piece with its crown level with the soil surface, firm the soil, and water well.

The Royal Horticultural Society’s advice on the last step is to plant divisions as soon as possible and water them in well. Its alternative, if the bed is not ready, is to pot the pieces up individually.

Root Types Change the Method

Penn State sorts perennials by root system, and the tool follows from the type.

Spreading roots. Tickseed, aster, bee balm, lamb’s ear and purple coneflower form mats of slender roots. These pull apart by hand or with a knife, and Clemson recommends clumps of three to five vigorous shoots each.

Clumping crowns. Astilbe, daylily, hosta and ornamental grasses grow from a dense central crown. Cut through the crown or pry it apart with two forks, keeping at least one developing eye or bud on each piece. Clemson notes that the very dense roots of ornamental grasses may call for an ax or saw.

Rhizomes. Bearded iris grows from thick stems at the soil surface. Penn State suggests dividing it in August, and Clemson gives a window from a month after flowering until early fall. Cut away and discard rhizome sections that are a year or more old, and replant the young pieces with the top of the rhizome just showing above soil level.

Tuberous roots. Dahlias and canna lilies are divided by cutting the clump of tubers apart, each piece keeping a bud.

A few popular plants have their own numbers in the Clemson fact sheet. Hostas divide into clumps with one to three eyes. Daylily divisions with three or more shoots bloom sooner. Peony divisions should carry three to five well-developed eyes, planted with the eyes no deeper than 1 inch below the surface.

Perennials You Can Divide, and How Often

Oregon State University Extension groups common perennials by how long they go between divisions.

Divide about every	Perennials
1 to 3 years	Shasta daisy, coral bells, phlox, penstemon, bee balm
3 to 5 years	Black-eyed Susan, daylily, catmint, coneflower
5 to 10 years	Hosta, Siberian iris, peony, lady’s mantle

Other sources give a single rule of thumb that lands inside those ranges. Penn State’s general recommendation is every three years, Clemson says most perennials need it every three to five years, and the RHS advises every two to three years to maintain health and vigor. Clemson singles out chrysanthemums and asters as needing division every one or two years, and notes that bleeding hearts and peonies may never need to be divided.

For ideas on what to plant with the extra divisions, see our list of low-maintenance perennials.

Perennials You Should Not Divide

Some perennials grow from a single taproot or a woody base and do not split cleanly. Penn State Extension’s do-not-divide list is lavender, Russian sage, butterfly weed, euphorbia, blue false indigo, baby’s breath, lupine, clematis and eastern columbine. Clemson’s list overlaps and adds oriental poppies, gas plant and Japanese anemones.

Clemson’s wording is that some plants resent being divided and it should be avoided if possible. Penn State says of butterfly weed and other single-taproot plants to leave them untouched.

Aftercare for New Divisions

Water is the main job. Water the divisions in at planting and keep the soil moist while new roots form. Dividing in a rainy spell does some of this for you.

Fall divisions need protection through their first winter in cold areas. Clemson recommends mulching fall-divided perennials in the South Carolina Upstate the first winter to prevent heaving, which it attributes to alternating shallow freezing and thawing of the soil. Penn State suggests a loose mulch such as straw. Our guide to choosing mulch for garden beds compares the materials.

If you replant in the same spot, the RHS suggests mixing in garden compost or another soil improver first, since the old clump has been drawing on that soil for years.