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Dividing Perennials

Dividing Perennials: A Rejuvenation Boost

When to Divide

While many perennials benefit from division every 3-5 years, it's essential to consider the plant's specific needs. Signs that a plant may need dividing include:

· Decreased flower production: Smaller or fewer blooms indicate potential overcrowding.

· Center die-back: A hollow or dead center suggests the plant needs rejuvenation.

· Crowded growth: Overcrowding can lead to weak stems and reduced vigor.

Plants That Benefit from Division

Perennials with fibrous or clump-forming root systems generally tolerate division well. Popular choices include: Daylilies, Irises, Hostas, Peonies, Phlox, Black-eyed Susans, Coneflowers

Plants to Avoid Dividing

It is best NOT to divide plants with woody crowns, a single stem/crown, fragile fleshy roots, or a tap root as doing so can damage the plant. This includes:

False indigo - Baptisia
Heartleaf brunnera - Brunnera
Clematis
Baby’s breath - Gypsophila
Coral bells - Heuchera
Foamy bells - Heucherella
Rose mallow - Hibiscus
Red hot poker - Kniphofia
Lavender - Lavandula
Beardtongue - Penstemon
Russian sage - Perovskia

Division Process

Timing: Divide perennials in spring or fall, See below for recommend times by Genus.
Preparation: Water the plant thoroughly a day before dividing.
Digging: Carefully dig up the entire clump.
Division: Use a sharp spade or hands to separate the plant into sections, ensuring each division has roots and shoots.
Replanting: Plant the divisions immediately in prepared soil.

Perennials with fibrous or loose root systems are the easiest kind to divide. Siberian irises, for example, can often be pulled apart with your hands once you have dug them up and shaken the soil off the roots. Ornamental onions like ‘Serendipity’ are similarly easy to pull apart and divide. Daylily roots are a little tougher to pull apart but can be cut with a sharp knife. Bee balm and spike speedwell are also easy to divide with a knife. Perennials with fibrous or loose root systems are the easiest kind to divide. Siberian irises, for example, can often be pulled apart with your hands once you have dug them up and shaken the soil off the roots. Ornamental onions like ‘Serendipity’ are similarly easy to pull apart and divide. Daylily roots are a little tougher to pull apart but can be cut with a sharp knife. Bee balm and spike speedwell are also easy to divide with a knife.

As a general guideline, perennials should be divided in the opposite season of which they bloom. That means if they bloom early in the season they should be divided in fall, and if they bloom late, they should be divided in spring. When you do so, dig up the whole clump of the perennial you want to divide so you can easily see its root system. Each piece you pull or cut away from the original clump should be no smaller than what would fit in a 1-quart (4-6”) pot. Immediately replant the divided pieces into the garden or containers before their roots dry out.

A note about dividing patented plants: Many varieties of perennial plants are protected under U.S. and Canadian patent laws. If a variety is patented or has a patent pending, that will be stated in small print on the plant label. In such cases, it is illegal to divide or propagate and sell that plant. This will not impact most home gardeners, but if you participate in local garden club plant sales, sell your plants online or something similar, you should know that it is illegal divide any patented or patent pending plants and sell them at such sales or for any other monetary gain.

Dividing Perennials

Dividing perennials rejuvenates the plants and gives you more to plant or share. It encourages new growth, improves flowering, and controls plant size.

Key Considerations When Dividing

Timing is crucial: Divide spring and early summer bloomers in the fall, and fall bloomers in the spring. This allows the plant to focus its energy on root and leaf growth.
Avoid stress: Don't divide on hot, sunny days. Choose a cool, cloudy day, ideally after a light rain.
Tool selection: Use a sharp spade or garden fork for most perennials. For plants with tough roots, a knife, saw, or even a hatchet may be necessary.
Division techniques: Some plants can be gently pulled apart, while others need to be cut. Always ensure each division has healthy roots and shoots.
Post-division care: Water your divided plants thoroughly and keep them consistently moist until they are established.

Plant - Specific Dividing Guide

Achillea spp. (Yarrow)

How often: Every 1 to 3 years
When: Spring
How: Cut or pull apart. Discard the central woody core.

Aegopodium podagraria 'Variegatum' (Snow-on-the-Mountain)

How often: Every 1 to 3 years
When: Spring or Fall
How: Lift the plant and divide it into sections, ensuring each has roots and shoots.

Ajuga reptans (Bugleweed)

How often: Every 1 to 3 years
When: Spring or Fall (can be divided almost any time)
How: Gently pull apart rooted sections or use a spade to separate.

Alchemilla mollis (Lady's Mantle)

How often: Every 6 to 10 years
When: Spring (or Early Fall)
How: Cut the crown into sections with a sharp spade or knife.

Allium spp. (Ornamental Onion)

How often: Every 2 to 3 years
When: Fall or Spring (after foliage dies back)
How: Lift the bulbs and separate the clusters. Replant in the fall.

Anemone spp. (Anemone)

How often: Every 10+ years (resents disturbance)
When: Spring
How: Carefully lift and divide the plant, minimizing root damage.

Aquilegia spp. (Columbine)

How often: Every 10+ years (does not like to be disturbed)
When: Spring (or Late Summer)
How: Dig deep to get all the roots. Cut young plants apart with a sharp knife.

Arisaema triphylla (Jack-in-the-Pulpit)

How often: When offsets form
When: Fall (when dormant)
How: Carefully separate the offsets from the main tuber.

Armeria spp. (Thrift)

How often: Every 4 to 5 years
When: Spring
How: Lift the plant and divide into sections with roots and shoots.

Artemisia spp. (Artemisia)

How often: Every 4 to 5 years
When: Spring
How: Divide and replant healthy outer sections. Discard the weak central crown.

Aruncus dioicus (Goats Beard)

How often: Every 10+ years (resents disturbance)
When: Spring or Fall
How: Use a knife to cut the woody crown into sections.

Asarum spp. (Ginger)

How often: Every 6 to 10 years
When: Spring or Early Fall
How: Use a sharp knife to cut the rhizome.

Asclepias spp. (Milkweed)

How often: Every 10+ years (does not like to be disturbed)
When: Spring
How: Dig deep to avoid damaging taproots. Cut the crown apart with a sharp knife.

Aster spp. (Aster)

How often: Every 1 to 3 years
When: Spring or Fall
How: Replant small, healthy pieces from the outside of the clump.

Astilbe x arendsii (Astilbe)

How often: Every 1 to 3 years
When: Spring (or Fall)
How: Cut the plant into sections with a sharp spade or knife.

Astrantia spp. (Masterwort)

How often: Every 4 to 5 years
When: Spring or Fall
How: Divide with a spade or pitchfork.

Athyrium filix-femina (Lady Fern)

How often: As needed
When: Spring or Fall
How: Use a sharp knife to cut the rootstock.

Athyrium niponicum (Japanese Painted Fern)

How often: As needed
When: Spring or Fall
How: Use a sharp knife to cut the rootstock.

Aubrieta deltoidea (Rockcress)

How often: Every 2 to 3 years
When: Spring
How: Lift the plant and divide into sections with roots and shoots.

Aurinia saxatilis (Basket of Gold)

How often: Every 3 to 4 years
When: Spring
How: Carefully divide the clump, as it can be difficult due to its dense growth habit.

Baptisia australis (False Blue Indigo)

How often: Every 10+ years (resents disturbance)
When: Spring
How: Dig deep to remove the entire root system. Cut the crown apart with a sharp knife or saw.

Bergenia cordifolia (Heart Leaf Bergenia)

How often: Every 4 to 5 years
When: Spring or Summer
How: Cut the rhizome with a sharp knife.

Boltonia asteroides (Boltonia)

How often: Every 4 to 5 years
When: Spring or Early Fall
How: Lift the plant and divide into sections.

Brunnera macrophylla (False Forget-me-not)

How often: Every 6 to 10 years
When: Spring or Fall (Late Summer)
How: Lift the plant and divide into sections.

Caltha palustris (Marsh Marigold)

How often: Every 3 to 4 years
When: After flowering (May or June)
How: Divide the plant into sections.

Campanula spp. (Bellflower)

How often: Every 4 to 5 years
When: Spring or Late Summer (August)
How: Cut the thick rootstock apart with a sharp knife.

Carex spp. (Sedge)

How often: As needed
When: Spring
How: Divide with a spade or pitchfork.

Catanache caerulea (Cupid's Dart)

How often: Every 1 to 3 years
When: Fall or Spring
How: Lift the plant and divide into sections.

Centaurea montana (Cornflower)

How often: Every 1 to 3 years
When: Spring (or Fall)
How: Lift the plant and divide into sections.

Cerastium tomentosum (Snow-in-Summer)

How often: Every 1 to 3 years
When: Spring or Fall (can be divided almost any time)
How: Gently pull apart or divide with a spade.

Chelone spp. (Turtlehead)

How often: Every 4 to 5 years
When: Spring
How: Dig with a spade to sever young offshoots from the parent plant.

Cimicifuga racemosa (Snakeroot or Bugbane)

How often: Every 10+ years (resents disturbance)
When: Spring
How: Cut the plant into sections with a sharp knife or spade. Discard the old, woody

Clematis spp. (Clematis)

How often: Every 10+ years (division is only necessary for certain species)
When: Spring
How: Cut the crown apart with a sharp knife or spade.

Convallaria majalis (Lily of the Valley)

How often: As needed to control spread
When: Spring or after flowering
How: Lift and divide the rhizomes.

Coreopsis (Tickseed)

How often: Every 1 to 3 years
When: Spring (or Early Fall)
How: Cut the crown apart with a sharp knife.

Delphinium grandiflorum (Delphinium)

How often: Every 1 to 3 years
When: Spring
How: Carefully lift and divide the plant.

Dendranthema x grandiflora (Garden Mum)

How often: Every year
When: Spring
How: Divide and replant, discarding the central core.

Dianthus spp. (Pinks)

How often: Every 1 to 3 years
When: Spring
How: Lift the plant and divide into sections.

Dicentra spp. (Bleeding Heart)

How often: Every 6 to 10 years
When: Spring
How: Cut the crown apart with a sharp knife, handling the brittle roots carefully.

Dictamnus albus (Gas Plant)

How often: Every 10+ years (division is difficult)
When: Spring
How: A spade plunged straight down through the plant's center can be used to divide the roots.

Dodecatheon meadia (Shooting Star)

How often: Every few years
When: Fall (or Spring)
How: Lift and divide the plant.

Echinacea purpurea (Purple Coneflower)

How often: Every 4 to 5 years
When: Spring (or Early Fall)
How: Cut the crown apart with a sharp knife.

Echinops ritro (Globe Thistle)

How often: Every 6 to 10 years (resents disturbance)
When: Spring (or Fall)
How: Carefully lift and divide the plant.

Epimedium x rubrum (Red Barrenwort)

How often: Every 6 to 10 years
When: Spring or Fall
How: Lift and divide the plant.

Eupatorium purpureum (Joe Pye Weed)

How often: Every 1 to 3 years
When: Spring to Early Fall
How: Use a knife to slice the woody crown.

Euphorbia polychroma (Cushion Spurge)

How often: Every 10+ years
When: Spring (or Fall)
How: Discard the central woody clump. Handle the roots carefully, as they can be brittle.

Gaillardia x grandiflora (Blanket Flower)

How often: Every 3 to 5 years
When: Spring or Fall
How: Divide by hand.

Galium odoratum (Sweet Woodruff)

How often: As needed to control spread
When: Spring (or Fall)
How: Divide by hand.

Geranium spp. (Cranesbill)

How often: Every 6 to 10 years
When: Spring (or Early Fall)
How: Some varieties can be pulled apart, while others need to be cut with a sharp knife.

Geum triflorum (Prairie Smoke)

How often: Every 1 to 3 years
When: After flowering in late summer
How: Lift the plant and divide into sections.

Grasses (Ornamental)

How often: When the center starts to die out
When: Spring
How: Discard the old, central portion. Use a sharp knife or spade for smaller grasses, and a hatchet or ax for larger ones.

Gypsophila paniculata (Baby's Breath)

How often: Every 10+ years (resents disturbance)
When: Spring
How: Double-flowered cultivars are grafted and cannot be divided.

Helenium autumnale (Sneezeweed, Helen's Flower)

How often: Every 1 to 3 years
When: Spring (or Fall)
How: Lift the plant and divide into sections.

Helianthus spp. (Sunflower)

How often: Every 1 to 3 years
When: Spring or Fall
How: Divide to improve performance and control invasiveness.

Heliopsis helianthoides (False Sunflower)

How often: Every 5 to 10 years
When: Spring (or Fall)
How: Cut the crown apart with a sharp knife. Discard the old central portion.

Helleborus orientalis (Lenten Rose)

How often: Every 10+ years
When: Spring (while in bloom or immediately after)
How: Carefully lift and divide the plant.

Hemerocallis spp. (Daylily)

How often: Every 3 to 5 years
When: Spring or immediately after flowering
How: Lift the plant and divide the fans.

Heuchera sanguinea (Coral Bells)

How often: Every 1 to 3 years
When: Spring (or Fall)
How: Cut the crown apart with a sharp knife. Discard the old, woody central portion.

Hibiscus moscheutos (Rose Mallow, Hibiscus)

How often: Every 10+ years
When: Spring or Fall
How: Lift and divide the plant.

Hosta spp. (Hosta)

How often: Every 6 to 10 years
When: Spring or Fall
How: If the center of the plant is bare, cut it out and discard it. Divide the remaining sections.

Hyssopus officianalis (Hyssop)

How often: Every 3 to 4 years
When: Spring
How: Carefully divide the woody roots.

Iris siberica (Siberian Iris)

How often: Every 6 to 10 years
When: Spring (before leaves are 3-4" tall) or Late Summer/Early Fall
How: Use a sharp knife to cut the rhizome.

Iris spp. (Bearded Iris)

How often: Every 1 to 3 years
When: 4 to 6 weeks after flowering
How: Use a sharp knife to cut the rhizome. Discard the older part of the plant.

Lamiastrum galeobdolen (Golden Deadnettle)

How often: As needed to control spread
When: Spring or Fall
How: Lift and divide the plant.

Lamium maculatum (Spotted Dead Nettle)

How often: Every 4 to 5 years
When: Spring (or mid-summer if cut back and watered well)
How: Lift and divide the plant.

Lathyrus latifolius (Perennial Sweet Pea)

How often: Every 10+ years (does not like to be disturbed)
When: Spring
How: Carefully lift and divide the plant.

Leucanthemum x superbum (Shasta Daisy)

How often: Every 1 to 3 years
When: Spring (or Fall)
How: Discard the old central portion.

Liatris spicata (Blazing Star, Gayfeather)

How often: Every 3 to 5 years
When: Spring
How: Cut into sections with a sharp knife.

Ligularia spp. (Ligularia)

How often: Every 6 to 10 years
When: Spring or Fall
How: Lift and divide the plant.

Lilium (Lily)

How often: Every 3 to 5 years
When: Late Summer / Early Fall
How: There are many types of lilies, each with specific division needs. Generally, you'll lift the bulbs and separate the scales or bulblets.

Limonium platyphyllum (Sea Lavender)

How often: Every 4 to 5 years
When: Spring or Early Fall
How: Carefully divide the long roots.

Linum perenne (Flax)

How often: Every 10+ years (does not like to be disturbed)
When: Spring (or Early Fall)
How: Dividing the long, tangled roots can be challenging.

Liriope spicata (Creeping Lilyturf)

How often: As needed to control spread
When: Spring or Fall
How: Use division to keep the invasive nature under control.

Lobelia cardinalis (Cardinal Flower)

How often: Every 1 to 3 years
When: Spring or Fall
How: Discard the old, central woody clump.

Lupinus 'Russell Hybrids' (Russell Hybrid Lupine)

How often: Every 10+ years (does not like to be disturbed)
When: Spring
How: Carefully lift and divide the plant.

Lysimachia spp. (Loosestrife)

How often: Every 6 to 10 years
When: Spring (or Fall)
How: Lift and divide the plant.

Malva alcea 'Fastigiata' (Hollyhock Mallow)

How often: Every 1 to 3 years
When: Spring or Fall
How: Lift and divide the plant.

Matteuccia pensylvanica (Ostrich Fern)

How often: As needed
When: Spring
How: Divide the spreading rhizomes.

Mentha spp. (Mint)

How often: Every 3 to 5 years
When: Spring or Fall
How: Use division to keep the invasive nature under control.

Mertensia virginica (Bluebells)

How often: Every 3 to 4 years
When: Spring
How: Lift and divide the plant.

Monarda didyma (Bee Balm)

How often: Every 1 to 3 years
When: Spring
How: Discard the old central clump.

Myosotis spp. (Forget-me-Not)

How often: As needed
When: Spring
How: Divide by hand.

Nepeta spp. (Catmint)

How often: Every 3 to 4 years
When: Spring (or after the primary bloom period)
How: Cut into sections with a sharp knife or spade.

Oenothera spp. (Sundrops, Evening Primrose)

How often: Every 10+ years (most species do not divide well)
When: Spring (or Fall)
How: Oenothera fruticosa needs more frequent division (every 1 to 3 years).

Onoclea sensibilis (Sensitive Fern)

How often: Rarely needs division
When: Spring or Fall
How: Divide the rhizomes.

Osmunda spp. (Fern - Cinnamon)

How often: As needed
When: Spring (or Fall)
How: Divide the rhizomes.

Pachysandra terminalis (Japanese Spurge)

How often: As needed to control spread
When: Spring
How: Lift and divide the plant.

Paeonia sp. (Peony)

How often: Every 10+ years (does not like to be disturbed)
When: Early Fall (Mid-August to September)
How: Dig around the plant and slit the roots with a sharp spade. Handle the thick, brittle roots carefully.

Papaver orientale (Oriental Poppy)

How often: Every 6 to 10 years (resents disturbance)
When: Mid- to Late Summer
How: Carefully lift and divide the plant, minimizing root damage.

Penstemon digitalis (Smooth Penstemon)

How often: Every 1 to 3 years
When: Spring
How: Divide with a spade or pitchfork.

Perovskia atriplicifolia (Russian Sage)

How often: Every 10+ years (does not like to be disturbed)
When: Spring or Fall
How: Carefully lift and divide the plant.

Phlox paniculata (Tall Phlox)

How often: Every 2 to 4 years
When: Spring (or Late Summer)
How: Discard the central core if woody or dead.

Phlox subulata (Creeping Phlox)

How often: Every 1 to 3 years
When: Spring or Early Fall
How: Use only non-woody stems for cuttings.

Physostegia virginiana (Obedient Plant)

How often: Every 1 to 3 years
When: Spring
How: Lift and divide the plant.

Platycodon grandiflorus (Balloon Flower)

How often: Every 10+ years (does not like to be disturbed)
When: Spring
How: Handle the brittle root system carefully.

Polemonium coeruleum (Jacob's Ladder)

How often: Every 6 to 10 years
When: Spring
How: Divide by hand.

Polygonatum odoratum (Solomon's Seal)

How often: Every 6 to 10 years
When: Spring or Fall
How: Slice through the knobby rootstock with a knife.

Polygonum cuspidatum (Fleeceflower)

How often: As needed to control spread
When: Spring or Fall
How: Lift and divide the plant.

Primula sp. (Primrose)

How often: Every few years
When: Spring after flowering or Early Fall
How: Divide by hand.

Pulmonaria spp. (Lungwort)

How often: Every 6 to 10 years
When: Spring after flowering (or Fall)
How: Lift and divide the plant. Water regularly after dividing.

Pulsatilla vulgaris (Pasque Flower)

How often: Every 10+ years (does not like to be disturbed)
When: Spring or Fall
How: Handle the fragile roots with care to avoid damage.

Rheum palmatum (Ornamental Rhubarb)

How often: Every 4 to 6 years
When: Spring
How: Use a sharp knife to cut the rootstock. Make sure each division has a dormant eye (crown bud).

Rudbeckia spp. (Black-Eyed Susan)

How often: Every 4 to 5 years
When: Spring (or Fall)
How: Divide with a spade or pitchfork.

Salvia spp. (Sage)

How often: Every 6 to 10 years
When: Spring (or Fall)
How: Divide when the plant dies out in the center.

Sanguisorba obtusa (Burnet)

How often: Every 4 to 5 years
When: Spring or Late Summer
How: Lift and divide the plant.

Saponaria ocymoides (Soapwort)

How often: As needed
When: Any time during the warmer months
How: Lift and divide the plant.

Scabiosa columbaria (Pincushion Flower)

How often: Every 4 to 5 years
When: Spring
How: Lift and divide the plant.

Sedum spp. (Stonecrop)

How often: Every 4 to 5 years
When: Spring
How: Divide by hand.

Sempervivum tectorum (Hen & Chicks)

How often: Whenever the plant has formed a good cluster of chicks
When: Spring or Fall
How: Separate the small outer rosettes ("chicks") from the parent plant.

Sidalcea spp. (Dwarf Hollyhock, False Mallow)

How often: Every 1 to 3 years
When: Spring or Fall
How: Lift and divide the plant.

Solidago spp. (Goldenrod)

How often: Every 4 to 5 years
When: Spring or Fall
How: Divide with a spade or pitchfork.

Stachys byzantina (Lamb's Ears)

How often: Every 4 to 5 years
When: Spring (or Fall)
How: Divide by hand.

Tanacetum coccineum (Painted Daisy)

How often: Every 1 to 3 years
When: Spring or Late Summer
How: Lift and divide the plant.

Thalictrum spp. (Meadow Rue)

How often: Every 6 to 10 years
When: Spring
How: Most species are slow to recover after division, so handle with care.

Thermopsis spp. (False Lupine)

How often: Every 10+ years (resents disturbance)
When: Spring
How: Only divide when plants are several years old.

Thymus spp. (Thyme)

How often: Every 4 to 5 years
When: Spring
How: Lift and divide the plant.

Tiarella wherryi (Foamflower)

How often: Every 1 to 3 years
When: Spring (or Fall)
How: Divide by hand.

Tradescantia x andersoniana (Spiderwort)

How often: Every 3 to 5 years
When: Spring (until flowers set)
How: Lift and divide the plant.

Tricyrtis hirta (Toad Lily)

How often: Every 6 to 10 years
When: Spring
How: Lift and divide the plant.

Trillium grandiflorum (Trillium)

How often: Every 10+ years (does not like to be disturbed)
When: Spring or Late Summer
How: Carefully lift and divide the plant.

Trollius chinensis (Globe Flower)

How often: Every 5 to 7 years
When: Fall
How: Lift and divide, being mindful that it's slow to recover from transplanting.

Veronicastrum virginicum (Culver's Root)

How often: Every 4 to 5 years
When: Spring or Late Summer
How: Lift and divide the plant.

Veronica spp. (Speedwell)

How often: Every 3 to 5 years
When: Spring or Early Fall
How: Lift and divide the plant.

Vinca minor (Periwinkle)

How often: As needed to control spread
When: Spring or Fall
How: Lift and divide the plant, or take cuttings.

Viola spp. (Violet)

How often: As needed
When: Spring or Fall
How: Divide by hand.

Waldsteinia ternata (Barren Strawberry)

How often: As needed to control spread
When: Spring (or Early Fall)
How: Division is safest when the plant is not blooming.

Yucca filamentosa (Adam's Needle, Ivory Tower, Yucca)

How often: Every 10+ years (resents disturbance)
When: Spring
How: Divide only young plants. Established plants have deep, thick roots that are difficult to divide.

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Dividing Perennials

Dividing Perennials: A Rejuvenation Boost