Open Grow Guide

Dividing perennials

By Open Grow Guide Updated

Dividing a perennial means lifting the clump, splitting it into pieces, and replanting them. Most perennials should be divided every three to five years. Chrysanthemums and asters may need it every one or two years, while bleeding hearts and peonies may never need it unless you want more plants. Overcrowded plants compete for nutrients and water, which is a reason to divide them before they decline. A clump that is growing and blooming well can stay as it is. This guide covers the signs, the timing, the tools, the digging, and the replanting.

When to do it

Timing depends on when the plant flowers. Perennials that bloom in summer or fall are divided in spring, while spring bloomers are divided after flowering or in fall. Bearded iris can be divided any time from a month after flowering until early fall. Hostas can be divided every 3 to 5 years in early spring as the leaves emerge from the ground.

Daylilies can be divided every 3 to 6 years, or as desired, to increase stock. Coral bells are usually short-lived unless they are divided regularly, about every 3 or 4 years. Garden mums can be divided in spring every few years to prevent the plants from becoming congested.

A decline marked by fewer or smaller flowers and sometimes yellowing leaves signals that it is time. Divide a perennial before it declines, rather than waiting until it is going downhill.

What you need

Start with a sharp spade or spading fork for digging around the clump. A shovel is useful when a clump is too heavy to lift whole and must be cut into pieces in place. Two forks used back-to-back will split a dense clump.

Roots that spread can be cut apart with a knife or shears. A sharp, heavy knife is used to cut clumping-root perennials apart. Tough, woody roots, as on hosta or ornamental grasses, may call for a garden fork, handsaw, or ax.

Keep a sharp knife or pruners on hand to trim broken or damaged roots before replanting. A hose can wash loose soil off the lifted clump. A pail of water, or a spot under cover, keeps divisions shaded and moist until you replant them. For fall divisions, have a loose, open mulch such as straw, pine straw, or leaves ready.

Step by step

  1. Step 1

    Choose a cloudy, overcast day to divide, ideally one with light rain in the forecast

    Avoid dividing on a hot, sunny day, since that can dry out the divided plants.

  2. Step 2

    Water the plant thoroughly a day or two before you divide it

    This matters most if the soil is already dry.

  3. Step 3

    Cut back the plant's stems and foliage to about 6 in (15 cm) from the ground before you divide it

    Do this before you prepare the planting holes or dig up the clump.

  4. Step 4

    Prepare the new planting holes before you dig up the clump

    Make each hole wide enough for the roots, and deep enough that the crown will sit level with the soil surface.

  5. Step 5

    Dig around the plant with a sharp spade or spading fork

    Dig about 4 to 6 in (10-15 cm) out from the crown, along its natural drip line.

  6. Step 6

    Lift the whole clump out of the ground in one piece

    Pry or lever underneath it with the spade or fork first.

  7. Step 7

    Cut an oversized clump into pieces while it's still in the hole, if it's too heavy to lift whole

    Use a shovel to divide it into smaller sections before lifting each piece out.

  8. Step 8

    Shake or hose the loose soil off the lifted clump

    Remove dead leaves and stems, and cut away the dead or weak center of the plant.

  9. Step 9

    Separate spreading-root plants by pulling the roots apart by hand, or by cutting them with a knife or shears

    For a dense, tangled clump, push two forks back-to-back into the center and pull the handles apart to split it.

  10. Step 10

    Give each spreading-root division three to five vigorous shoots, along with a healthy share of roots

    As a general rule, make sure every division has at least two growing points.

  11. Step 11

    Cut clumping-root perennials apart with a sharp, heavy knife

    Keep at least one developing eye, or bud, on each division, and leave several eyes if you want larger plants sooner.

  12. Step 12

    Cut apart tough, woody roots with a sharp knife, garden fork, handsaw, or ax

    Hosta and ornamental grasses are examples of perennials with roots tough enough to need this approach.

  13. Step 13

    Raise a heavy, tangled clump 1 to 2 ft (30-60 cm) off the ground and drop it

    This can separate roots that are too matted to pull apart by hand. Skip this method on plants with brittle roots, such as peonies, since dropping can break them.

  14. Step 14

    Keep the lifted divisions shaded and moist until you can replant them

    A pail of water or any kind of cover works well for a short wait.

  15. Step 15

    Discard any small, weak, or woody divisions instead of replanting them

    Save your effort for divisions that look vigorous and healthy.

  16. Step 16

    Trim any broken or damaged roots with a sharp knife or pruners before replanting

    Do this right before you put the division back in the ground.

  17. Step 17

    Replant each division at the same depth it was growing at before

    Peony divisions are an exception. Plant them only about 1 to 1.5 in (2.5-4 cm) below the soil surface. Planting them deeper can stop the plant from flowering.

  18. Step 18

    Plant iris rhizome divisions with the top of the rhizome showing just above the soil

    Trim the fan of leaves back by about half.

  19. Step 19

    Firm the soil around the roots of each newly planted division

    This gets rid of any air pockets around the roots.

  20. Step 20

    Water the new divisions well right after you plant and firm the soil

    This is the last step before the divisions settle into their new spot.

  21. Step 21

    Mulch divisions planted in fall for their first winter

    Use a loose, open material, such as straw, pine straw, or leaves, to stop the plants from heaving out of the ground.

  22. Step 22

    Hold off on fertilizing newly divided plants

    Give them time to grow new roots first.

  23. Step 23

    Shade newly replanted divisions if they're hit by unexpected hot sun

    Avoid overwatering them, since too much water promotes root rot and fungal growth.

Mistakes to avoid

Dividing a plant while it is blooming is a common error. The plant should put its energy into regenerating root and leaf tissue instead of flowers. Dividing on a hot, sunny day can cause the divided plants to dry out. In fall, dividing too late leaves roots without time to become established, so finish at least four to six weeks before the ground freezes.

Planting too deep is another fault. Peony divisions belong only about 1 to 1.5 in (2.5-4 cm) below the soil surface, and planting them deeper can prevent flowering. Overwatering new divisions promotes root rot and fungal growth. Fertilizing right away is also a mistake, because new divisions need time to grow new roots first.

Some plants should not be divided at all. Lavender, rosemary, and similar woody-based perennials are actually small shrubs, and woody artemisias should not be divided either. Plants with a single taproot, such as butterfly weed, resent being divided. Lenten and Christmas roses become very difficult to move once they are more than a few years old.

Dividing an entire garden at once is a further error, so spread the work over several years. Do not replant small, weak, or woody divisions.

How this page was made

  • Written with AI assistance from the sources listed on this page. AI is never the source of a fact.

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