Dividing Perennials

Description:

Perennials grace our gardens year after year with their variety of brilliant colors and unique foliage forms. After a few years in the garden, however, these perennials may start to produce smaller blooms, develop a 'bald spot' at the center of their crown, or require staking to prevent their stems from falling over. All of these are signs that it is time to divide. However, reduced plant performance may not be the only reason to divide perennials.

Why Divide Perennials?

There are three main reasons to divide perennials:

1. To rejuvenate the plant and stimulate new growth.
Overcrowded plants compete for nutrients and water. Restricted airflow can lead to diseases. Dividing the plants into smaller sections reduces this competition and stimulates new growth as well as more vigorous blooming.

2. To control the size of the plant.
Since plants grow at varying rates, division may be used to keep plants that spread rapidly under control.

3. To increase the number of plants.
Division is an easy and inexpensive way to increase the number of plants in your garden.

Guidelines for Dividing Perennials:

There are a couple things to keep in mind to make the most of perennial propagation. It is best to divide perennials on cloudy, overcast days. Dividing on a hot sunny day can cause the plants to dry out. Water the soil a day in advance if the area to be worked on is dry. Ideally, division should be done when there are a couple days of showers in the forecast to provide adequate moisture for the newly transplanted divisions.

To divide perennials, dig up the parent plant using a spade or fork. Gently lift the plant out of the ground and remove any loose dirt around the roots. Separate the plant into smaller divisions by teasing the roots apart or cutting them with a sharp knife or spade. Plants may also be separated by placing two forks in the center of the clump back to back and pulling them apart. Each division should have 3 to 5 vigorous shoots and a healthy supply of roots. Keep these divisions shaded and moist until they are replanted.

For more specific information on how to divide specific types of perennials, visit Clemson Extension page on Dividing Perennials.

Timing of Divisions

When it comes to the timing of perennial division, a general rule to follow is to divide spring and summer blooming perennials in the fall and fall blooming perennials in the spring. Dividing when the plant is not flowering allows all of its energy to focus on regenerating root and leaf tissue.

Spring division should occur just as new growth is emerging. By working on the plant at this time, it is easier to see what you're doing and the smaller leaves and shoots won't suffer as much damage as full-grown leaves and stems. Spring is also a good time to divide because the plants have stored up energy in their roots which will aid in their recovery. Another benefit of spring is the rain showers that generally come along with the early season. Spring division also allows the plants an entire growing season to recover before the onset of winter.

Fall division has its own benefits. Because there are so many gardening tasks to be performed in the spring, dividing plants in the fall can help to even out some of the workload. Another benefit to fall division that there is no problem locating the plants to be divided. Perennials with fleshy roots such as peonies (Paeonia spp.), Oriental poppy (Papaver orientale), and Siberian iris (Iris siberica) are best divided in the fall. When dividing plants in the fall, allow four to six weeks before the ground freezes for the plants roots to become established. This is particularly important in colder, northern climates.

The following chart goes into more detail on the timing of perennial divisions. For each perennial, it provides information on how often it should be divided as well as what time of year is best for division. Some plants, like Russian sage (Perovskia atriplicifolia), don't like to be disturbed. These should only be divided to increase the number of plants. Any information specific to the division of a particular perennial has also been included.

Scientific name

Name

How often to divide

When to divide

Addition Notes

Achillea spp.

Yarrow

1 to 3 years

Spring

Separate by cutting or pulling apart. Discard central woody core.

Acontium napellus

Monkshood

10+ years

Spring

Resents disturbance. Due to poisonous nature of roots, use rubber gloves when dividing tuberous roots.

Adiantum pedatum

Maidenhair Fern

Spring

Aegopodium podagraria 'Variegatum'

Snow-on-the-Mountain

1 to 3 years

Spring or Fall

Ajuga reptans

Bugleweed

1 to 3 years

Spring or Fall

Can be divided any time of year, but spring and fall are best for quick rooting.

Alchemilla mollis

Lady's Mantle

6 to 10 years

Spring (or Early Fall)

Cut crown into sections with sharp spade or knife.

Allium spp.

Ornamental Onion

Fall

Divide overcrowded clusters after foliage disappears. Plant "new" bulbs in fall.

Anemone spp.

Anemone

10+ years

Spring

Resents disturbance.

Aquilegia spp.

Columbine

10+ years

Spring (or Late Summer)

Does not like to be disturbed. Dig deep to get all tapering, finger-like roots. Cut young plant apart with a sharp knife.

Arisaema triphylla

Jack-in-the-Pulpit

Fall

Divide offsets when plant is dormant

Armeria spp.

Thrift

4 to 5 years

Spring

Artemisia spp.

Artemisia

4 to 5 years

Spring

Regular division is important for health of plant and helps keep its invasive nature under control. Discard weak central crown.

Aruncus dioicus

Goats Beard

10+ years

Spring or Fall

Deep rootstock resents disturbance. Use knife to cut woody crown.

Asarum spp.

Ginger

6 to 10 years

Spring or Early Fall

Use sharp knife to cut rhizome.

Asclepias spp.

Milkweed

10+ years

Does not like to be disturbed. Dig deep to avoid damaging deep taproots. Cut crown apart with sharp knife. Rootstocks are brittle.

Aster spp.

Aster

1 to 3 years

Spring or Fall

Many cultivars require frequent division and replanting of small, healthy pieces from the outside of the clump.

Astilbe x arendsii

Astilbe

1 to 3 years

Spring (or Fall)

Needs division for best bloom. Cut plant into sections with sharp spade or knife.

Astrantia spp.

Masterwort

4 to 5 years

Spring or Fall

Divide with spade or pitchfork.

Athyrium filix-femina

Lady Fern

Spring or Fall

Use sharp knife to cut rootstock.

Athyrium niponicum

Japanese Painted Fern

Spring or Fall

Use sharp knife to cut rootstock.

Aubrieta deltoidea

Rockcress

Spring

Aurinia saxatilis

Basket of Gold

Spring

Difficult because plants clump

Baptisia australis

False Blue Indigo

10+ years

Spring

Resents disturbance. Dig deep to remove entire root system without breaking it. Cut crown apart with sharp knife or saw.

Bergenia cordifolia

Heart Leaf Bergenia

4 to 5 years

Spring or Summer

Cut rhizome with sharp knife. Transplant divisions fairly deep into soil.

Boltonia asteroides

Boltonia

4 to 5 years

Spring or Early Fall

Brunnera macrophylla

False Forget-me-not

6 to 10 years

Spring or Fall (Late Summer)

Caltha palustris

Marsh Marigold

After flowering - May or June

Campanula spp.

Bellflower

4 to 5 years

Spring or Late Summer (August)

Cut thick, fleshy rootstock apart with sharp knife.

Carex spp.

Sedge

Spring

Divide with spade or pitchfork.

Catanache caerulea

Cupid's Dart

1 to 3 years

Fall or Spring

Centaurea montana

Cornflower

1 to 3 years

Spring (or Fall)

Cerastium tomentosum

Snow-in-summer

1 to 3 years

Spring or Fall

Can be divided virtually anytime.

Chelone spp.

Turtlehead

4 to 5 years

Spring

When young offshoots are 1" high, dig with spade to sever from parent plant.

Cimicifuga racemosa

Snakeroot or Bugbane

10+ years

Spring

Resents disturbance. Cut plant into sections with sharp knife or spade. Discard old, woody, central clump.

Clematis spp.

Clematis

10+ years

Spring

Divisions on only selected species. Cut crown apart with sharp knife or spade.

Convallaria majalis

Lily of the Valley

Spring or After Flowering

Divide to keep invasive nature under control.

Coreopsis

Tickseed

1 to 3 years

Spring (or Early Fall)

Cut crown apart with sharp knife. Coreopsis grandiflora and Coreopsis lanceolata live longer if divided every 2 to 3 years.

Delphinium grandiflorum

Delphinium

1 to 3 years

Spring

Fall-dug plants often die over winter. Regular division can prolong their life.

Dendranthema x grandiflora

Garden Mum

Every year

Spring

Will survive longer and be most vigorous if divided and replanted every spring. Discard central core.

Dianthus spp.

Pinks

1 to 3 years

Spring

Dividing every few years can often extend longevity.

Dicentra spp.

Bleeding Heart

6 to 10 years

Spring

Cut crown apart with sharp knife. Roots are brittle, so handle carefully.

Dictamnus albus

Gas Plant

10+ years

Divisions are difficult due to crown damage. A spade plunged straight down through the plant's center, cutting the roots cleanly without severe bruising gives best results.

Dodecatheon meadia

Shooting Star

Fall (or Spring)

Echinacea purpurea

Purple Coneflower

4 to 5 years

Spring (or Early Fall)

Can remain undisturbed for years. Divide every 4 to 5 years for plant's health. Cut crown apart with sharp knife.

Echinops ritro

Globe Thistle

6 to 10 years

Spring (or Fall)

Resents disturbance.

Epimedium x rubrum

Red Barrenwort

6 to 10 years

Spring or fall

If conditions are favorable, can be left undisturbed for years.

Eupatorium purpureum

Joe Pye Weed

1 to 3 years

Spring to Summer/Early Fall

Use knife to slice woody crown.

Euphorbia polychroma

Cushion Spurge

10+ years

Spring (or Fall)

Discard central woody clump. Roots of some spurges are brittle, so handle carefully.

Gaillardia x grandiflorum

Blanket Flower

3 to 5 years

Spring or Fall

Divide by hand.

Galium odoratum

Sweet Woodruff

Spring (or Fall)

Divide by hand.

Geranium spp.

Cranesbill

6 to 10 years

Spring (or Early Fall)

Some varieties can be pulled apart by hand while others will need to be cut apart with a sharp knife.

Geum triflorum

Prairie Smoke

1 to 3 years

After flowering in late Summer

Grasses

Spring

Most grow well for years without division. Discard old, central portion of crown. Use sharp knife or spade to divide smaller grasses; use hatchet or ax on large grasses

Gypsophila paniculata

Baby's Breath

10+ years

Deep taproots resent disturbance. Double-flowered cultivars are grafted and, therefore, cannot be divided

Helenium autumnale

Sneezeweed, Helen's Flower

1 to 3 years

Spring (or Fall)

Helianthus spp.

Sunflower

1 to 3 years

Spring or Fall

Regular division improves performance and keeps invasive nature under control.

Heliopsis helianthoides

False Sunflower

5 to 10 years

Spring (or Fall)

Cut crown apart with sharp knife. Discard old central portion.

Helleborus orientalis

Lenten Rose

10+ years

Spring

Divide while plants are in bloom or immediately after they stop flowering.

Hemerocallis spp.

Daylily

3 to 5 years

Spring or immediately after flower

Division promotes heavier bloom.

Heuchera sanguinea

Coral Bells

1 to 3 years

Spring (or Fall)

Cut crown apart with sharp knife. Discard old, woody, central portion.

Hibiscus moscheutos

Rose Mallow, Hibiscus

10+ years

Spring or Fall

Plants are slow to send up shoots in spring, so fall division might be easier.

Hosta spp.

Hosta

6 to 10 years

Spring or Fall

If center of plant begins to get bare, cut out center and discard.

Hyssopus officianalis

Hyssop

Spring

Carefully divide woody roots.

Iris spp.

Bearded Iris

1 to 3 years

4 to 6 weeks after flowers are finished blooming

Fewer blooms indicate need for rejuvenation. Use a sharp knife to cut rhizome. Discard older part of plant.

Iris siberica

Siberian Iris

6 to 10 years

Spring* or Late Summer/Early Fall**

*In spring divide before leaves are 3" to 4" tall. Dividing too late can stop bloom for an entire season. **In early fall, cut leaves back to 6" to 12" and then divide. Use sharp knife to cut rhizome.

Lamiastrum galeobdolen

Golden Deadnettle

Spring or Fall

Lamium maculatum

Spotted Dead Nettle

4 to 5 years

Spring

Can also be divided mid-summer if cut back and watered well while taking root.

Lathyrus latifolius

Perennial Sweet Pea

10+ years

Spring

Does not like to be disturbed.

Leucanthemum x superbum

Shasta Daisy

1 to 3 years

Spring (or Fall)

Regular division can extend their life. Discard old central portion.

Liatris spicata

Blazing Star, Gayfeather

3 to 5 years

Spring

Cut into sections with sharp knife.

Ligularia spp.

Ligularia

6 to 10 years

Spring or Fall

Lilium

Lily

Late Summer / Early Fall

There are so many types of lilies, a whole book could be dedicated to how to divide each type.

Limonium platyphyllum

Sea Lavender

Spring or Early Fall

Carefully divide long roots.

Linum perenne

Flax

10+ years

Spring (or Early Fall)

Does not like to be disturbed. Dividing long, tangled roots is chancy.

Liriope spicata

Creeping Lilyturf

Spring or Fall

Use division to keep invasive nature under control.

Lobelia cardinalis

Cardinal Flower

1 to 3 years

Spring or Fall

Discard old central, woody clump.

Lupinus 'Russell Hybrids'

Russell Hybrid Lupine

10+ years

Spring

Does not like to be disturbed.

Lysimachia spp.

Loosestrife

6 to 10 years

Spring (or Fall)

Malva alcea 'Fastigiata'

Hollyhock Mallow

1 to 3 years

Spring or Fall

Matteuccia pensylvanica

Ostrich Fern

Spring

Mentha spp.

Mint

3 to 5 years

Spring or Fall

Use division to keep invasive nature under control.

Mertensia virginica

Bluebells

3 to 4 years

Spring

Monarda didyma

Bee Balm

1 to 3 years

Spring

Discard old central clump.

Myosotis spp.

Forget-me-Not

Spring

Divide by hand.

Nepeta spp.

Catmint

*Spring

Cut into sections with sharp knife or spade. * Can also be divided after primary bloom period if cut back and watered carefully.

Oenothera spp.

Sundrops, Evening Primrose

*10+ years

Spring (or Fall)

Most species do not divide well. Oenothera fruticosa needs to be divided every 1 to 3 years.

Onoclea sensibilis

Sensitive Fern

Spring (or Fall)

Osmunda spp.

Fern - Cinnamon

Spring

Pachysandra terminalis

Japanese Spurge

Spring

Paeonia sp.

Peony

10+ years

Early Fall Mid-August / September

Does not like to be disturbed. Dig around plant & slit roots with sharp spade. Roots are thick and brittle. Replanting too deep can diminish flowering.

Papaver orientale

Oriental Poppy

6 to 10 years

Mid- to Late Summer

Resents disturbance.

Penstemon digitalis

Smooth Penstemon

1 to 3 years

Spring

Divide with spade or pitchfork.

Perovskia atriplicifolia

Russian Sage

10+ years

Spring or Fall

Does not like to be disturbed.

Phlox paniculata

Tall Phlox

2 to 4 years

Spring (or Late Summer)

Discard central core if woody or dead.

Phlox subulata

Creeping Phlox

1 to 3 years

Spring or Early Fall

Use only non-woody stems.

Physostegia virginiana

Obedient Plant

1 to 3 years

Spring

Platycodon grandiflorus

Balloon Flower

10+ years

Spring

Does not like to be disturbed. Will not bloom for a year or two after division. Handle brittle root system carefully.

Polemonium coeruleum

Jacob's Ladder

6 to 10 years

Spring

Divide by hand.

Polygonatum odoratum

Solomon's Seal

6 to 10 years

Spring or Fall

Slice through knobby rootstock with knife.

Polygonum cuspidatum

Fleeceflower

Spring or Fall

Primula sp.

Primrose

Spring after flowering or Early Fall

Divide by hand.

Pulmonaria spp.

Lungwort

6 to 10 years

Spring after flowering (or Fall)

Water regularly following division

Pulsatilla vulgaris

Pasque Flower

10+ years

Spring or Fall

Does not like to be disturbed. Fragile roots may die if bruised.

Rheum palmatum

Ornamental Rhubarb

Spring

Use sharp knife to cut rootstock. Make sure each division has a dormant eye (crown bud).

Rudbeckia spp.

Black Eyed Susan

4 to 5 years

Spring (or Fall)

Divide with spade or pitchfork.

Salvia spp.

Sage

6 to 10 years

Spring (or Fall)

When plant dies out in center, it's time to divide.

Sanguisorba obtusa

Burnet

4 to 5 years

Spring or Late Summer

Saponaria ocymoides

Soapwort

Any time during warmer months

Scabiosa columbaria

Pincushion Flower

4 to 5 years

Spring

Division is a reliable but slow method of propagation.

Sedum spp.

Stonecrop

4 to 5 years

Spring

Divide by hand.

Sempervivum tectorum

Hen & Chicks

Spring or Fall

Separate small outer rosettes from parent plant.

Sidalcea spp.

Dwarf Hollyhock, False Mallow

1 to 3 years

Spring or Fall

Solidago spp.

Goldenrod

4 to 5 years

Spring or Fall

Divide with spade or pitchfork.

Stachys byzantina

Lamb's Ears

4 to 5 years

Spring (or Fall)

Divide by hand.

Tanacetum coccineum

Painted Daisy

1 to 3 years

Spring or Late Summer

Thalictrum spp.

Meadow Rue

6 to 10 years

Spring

Most species are slow to recover after division.

Thermopsis spp.

False Lupine

10+ years

Spring

Resents disturbance. Only divide when plants are several years old.

Thymus spp.

Thyme

4 to 5 years

Spring

Tiarella wherryi

Foamflower

1 to 3 years

Spring (or Fall)

Divide by hand.

Tradescantia x andersoniana

Spiderwort

3 to 5 years

Spring (until flowers set)

Division is only way to ensure duplication of cultivars.

Tricyrtis hirta

Toad Lily

6 to 10 years

Spring

Trillium grandiflorum

Trillium

10+ years

Spring or Late Summer

Does not like to be disturbed.

Trollius chinensis

Globe Flower

Fall

Slow to recover from transplanting.

Veronica spp.

Speedwell

3 to 5 years

Spring or Early Fall

Veronicastrum virginicum

Culver's Root

4 to 5 years

Spring or Late Summer

Vinca minor

Periwinkle

Spring or Fall

Viola spp.

Violet

Spring or Fall

Divide by hand.

Waldsteinia ternata

Barren Strawberry

Spring (or Early Fall)

Division is safest when plant is not blooming.

Yucca filamentosa

Adam's Needle, Ivory Tower, Yucca

10+ years

Resents disturbance. Divide only young plants. Established plants have deep, thick roots.

References:

Barrott, Susan. University of Minnesota Extension Service web site, "Yard & Garden Brief: Dividing Perennials," 1999. http://www.extension.umn.edu/projects/yardandgarden/ygbriefs/h140perennialdivide.html

Burns, Marilyn. The Southern Lakes Gardener web site, "Divide & Multiply: Dividing Perennials," 2003. http://www.gardengal.net/page120.html

DiSabato-Aust, Tracy. The Well-Tended Perennial Garden: Planting & Pruning Techniques. Oregon: Timber Press, 1998.

Heger, Mile & Whitman, John. Growing Perennials in Cold Climates. Illinois: Contemporary Books, 1998.

Hudak, Joseph. Gardening with Perennials Month by Month. Portland, OR: Timber Press, 1993.

Meier, Todd. The Taunton Press web site, "Techniques for Dividing Perennials." http://www.taunton.com/finegardening/pages/g00022.asp

Meier, Todd. The Taunton Press web site, "Dividing Perennials: Tools, Techniques and Timing." http://www.taunton.com/finegardening/pages/g00021.asp

Nau, Jim. Ball Perennial Manual: Propagation and Production. Illinois: Ball Publishing, 1996.

Still, Steven. Manual of Herbaceous Landscape Plants. Illinois: Stipes Publishing Company, 1994.

Russ, Karen. Clemson University Extension web site, "Dividing Perennials," 1999. http://hgic.clemson.edu/factsheets/HGIC1150.htm

Wood, Christopher. Encyclopedia of Perennials: A Gardener's Guide. New York: Facts on File, 1992.

Yockey, Terry. Northern Gardening web site, "Dividing Perennials," 2003. http://www.northerngardening.com/dividing.htm

This implementation report was developed by Molly Furgeson, student, University of Minnesota Department of Horticultural Science.