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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