13 Perennials You Should Never Divide

Plus, 14 perennials you should divide every few years, and our tips on how and when to do it.

By: Julie Martens Forney and Lynn Coulter

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Know Which Perennials to Divide and Which Ones to Leave Alone

An eye-catching border packed with season-long color makes any landscape sing, but some perennials need to be divided every few years to rejuvenate them. As a bonus, you'll wind up with more plants to add to your garden or share with friends. In general, clumping plants like daylilies or irises can be divided. Other perennials dislike being separated and should be left alone. Use our guide to keep your garden healthy, strong and beautiful. First up: Perennials you should not divide.

Lupine

In areas with cool summers, lupines are prized perennials that attract butterflies and hummingbirds. The secret to beautiful lupines is rich, slightly acidic soil that drains well. This deep, tap-rooted perennial doesn’t respond well to division or disturbance, so let plants set seeds instead. Seedlings don’t always come true to parent plants, so you might be surprised by the flower colors you see. Hardy in USDA Gardening Zones 4 to 6. Pictured: Lupinus Popsicle Series Mixed.

Lavender

Lavender is actually a woody shrub, which means it won’t respond well to division — your divisions will likely die. Instead, look around the plant for stems that might have layered. Layering occurs when branches that the touch soil develop roots. Cut the branch between the main plant and the layered seedling, dig up the seedling and treat it like a division. Pictured: Lavandula angustifolia 'Munstead'. 'Munstead' is one of the hardiest lavenders, surviving winters in Zones 5 to 9.

Learn More: How to Plant, Grow and Care for Lavender

Peony

Peonies are perennials that grow in the garden from generation to generation without missing a blooming beat. Dividing this perennial, which is hardy in Zones 3 to 9, isn’t recommended. If you must divide, do it in the fall and be sure to get at least three growing points, also called eyes, with each division. More eyes per division are better.

Learn More: Peony Flowers: How to Plant and Care for Peonies

Red Hot Poker

Spikes of blazing blooms in tones of red, orange and gold earn red hot poker its name. These perennials with narrow, evergreen foliage are conversation starters in the garden. 'First Sunrise' is an early-blooming variety — an ideal size for smaller modern gardens. Hummingbirds love the blossoms. Division doesn’t usually go well. Try to lift pups (baby plants growing nearby) or smaller plants from around the mother clump instead. Hardy in Zones 5 to 9. Pictured: Kniphofia 'First Sunrise'.

Baby’s Breath

Prized in floral arrangements, hardy baby's breath forms a flowery cloud in the garden. Its long taproot makes division very difficult, if not impossible. Trim plants back in spring before new growth starts. Count on baby’s breath as a filler in perennial gardens. The variety pictured (Gypsophila paniculata 'Danfestar' Festival Star) is shorter, topping out at 12 to 18 inches. It's a perfect choice for growing near the front of a flower border. Hardy in Zones 3 to 9.

Learn More: How to Plant and Enjoy Baby's Breath

Columbine

Plants flower in late spring to early summer, and they are rabbit-resistant. Columbine typically self-sows if blooms are allowed to set seed and the plants are hardy in Zones 3 to 9. This is the easiest way to propagate this perennial. Dividing mature plants doesn’t work. Pictured: Aquilegia x caerulea 'Sunshine'.

Learn More: How to Grow Columbine Flowers

Oriental Poppy

Poppies steal the show when they're in full bloom, but plants go dormant later. Tuck other perennials around them to avoid bare spots in the garden. Oriental poppies form long taproots that resemble white carrots. Dividing isn’t always successful and is not typically recommended. Hardy in Zones 3 to 7. Pictured: Papaver orientalis 'Flamenco Dancer' which unfurls 4- to 6-inch-wide red blossoms with deep black centers in late spring to early summer.

Learn More: How to Plant, Grow and Care for Poppy Flowers

Goat's Beard

For the partial shade garden, it's tough to beat the feathery flowers of goat's beard. This summer bloomer opens flower spikes up to 12 inches long. Plants are pest-free, deer-resistant and hardy in Zones 3 to 7. Place goat's beard where you want it — plants form thick roots that often require a saw to cut. It's best not to plan on dividing this shade-loving plant. Look for young shoots around the mother plant and attempt to transplant those.

Swamp Milkweed

A must in butterfly gardens, swamp milkweed is a host plant for monarch butterfly caterpillars. Butterfly adults visit blooms, along with many other pollinators. Flowers are typically pink, but you may spot some white blossoms on plants. Despite the name, swamp milkweed tolerates average to moist soils. This tap-rooted perennial prefers full sun and is best left undisturbed once planted in the garden. Swamp milkweed is hardy in Zones 3 to 6.

Learn More: Planting and Growing Milkweed

Blue False Indigo

Beautiful purple flower spikes appear in late spring to early summer above blue-tinted leaves on this shrubby native. Blue false indigo can be slow to establish in the garden and dislikes being moved, so take time to site it carefully. Give plants full sun and keep an eye out for caterpillars. Many butterflies use this plant as host food for their caterpillar larvae. False indigo is hardy in Zones 4 to 8.

Candytuft

Candytuft is a spring star, cascading over stone walls and slopes with blooming abandon. Its snow-white flowers sparkle in spring sunshine. This ground cover is actually a type of woody shrub, which is why it doesn’t divide well. 'Little Gem' (pictured) is smaller and grows more slowly than old-fashioned candytuft, making it a smart choice for low-maintenance modern landscapes. Plants are hardy in Zones 3 to 9.

Gas Plant

From late spring to midsummer, gas plant earns its keep in the garden with pink flower spikes. Butterflies flock to blooms, but deer avoid this perennial because of its lemon-scented leaves. Plants are hardy in Zones 3 to 7. Gas plant forms a deep tap root that makes division difficult. Instead, dig up seedlings that form around the mother plant. Gas plant sap irritates skin, so wear gloves when working with this perennial. Pictured: Dictamnus albus 'Purpureus'.

Russian Sage

For tough-as-nails beauty from late summer to fall, try Russian sage. This perennial loves hot, dry, full sun conditions and creates a cloud of purple in the garden when it flowers. Plants are a woody perennial that doesn’t divide well. Instead, transplant layered seedlings — plants that have formed where stems touched the soil and rooted. Leaves and stems have a sagey scent, which makes them distasteful to rabbits and deer. Plants are hardy in Zones 4 to 9.

Learn More: Planting and Growing Russian Sage

Perennials That Need Dividing Every Few Years

Some perennials don't mind being divided; in fact, they should be separated. If some of your perennials have stopped flowering, become crowded or start dying out, it may be time to reach for a sharp spade or knife. Browse our list of the most common blooms that need dividing every few years. Please note that even though all of these may benefit from more frequent division in ideal conditions, actual timing depends on your growing conditions and how fast the plants are growing.

Yarrow

If your yard is plagued with dry, lean or sandy soil, this is the bloomer for you. Deer and rabbits tend to leave yarrow alone. Divide the plants every two to three years in the spring. Achillea 'Moonshine' (pictured) boasts lemon yellow blooms atop plants that reach 12 to 24 inches tall. 'Moonshine' is hardy in Zones 3 to 8.

Learn More: Planting and Growing Yarrow

Speedwell

Fuss-free and easy-growing, speedwell thrives with minimal care when tucked in average, well-drained soil. Flower buds appear in May and keep coming all season long if you faithfully remove spent blossom spikes. Every three or four years, in early spring or fall, take divisions from the outer parts of the plants, not the older interior. Veronica 'Sunny Border Blue' (pictured) is hardy in Zones 5 to 9.

Astilbe

Dress up a shady, moist planting area with the feathery spikes of astilbe. The delicate-looking flowers belie this perennial's tough features, including deer and rabbit resistance. Divide the clumps when they become overcrowded, which shouldn't occur before the three-year mark in average growing conditions. The plants are hardy in Zones 4 to 8. Pictured: Astilbe 'Rise and Shine'.

Learn More: Growing Astilbe

Shasta Daisy

If you're a daisy lover, make room for Shasta daisy. Leucanthemum 'Daisy May' (pictured) boasts an earlier start to the flowering season and plants offer a compact form: 12 to 24 inches tall by 10 to 14 inches wide. Remove spent blooms for a second flower show in early autumn. Divide every three to five years after the blooms finish, when the plants start to drop leaves or show other signs of going dormant. Dig up entire plants and separate them into small clumps, making sure each clump has good roots. Hardy in Zones 5 to 9.

Learn More: Planting and Caring for Shasta Daisy

Coral Bells

Celebrate the beauty of colorful leaves by adding heuchera to your garden. The foliage of 'Plum Pudding' (pictured) blends shades of silver and purple that maintain a steady presence in planting beds all season long. Small flowers appear in late spring to early summer. Heuchera needs full sun to part shade in Northern zones; provide afternoon shade in Southern areas. In the spring, separate and replant divisions with the crowns at ground level. Plants are hardy in Zones 4 to 9.

Learn More: Planting Coral Bells: How to Grow and Care for These Colorful Perennials

Creeping Phlox

Convert a rock garden or slope into a carpet of spring color by planting creeping phlox, sometimes called moss phlox. This ground cover prefers gritty, alkaline soils in full sun, which means it thrives in planting beds along concrete sidewalks or driveways. Flowers bring long-lasting color to the garden. After blooms fade, trim any dead or weak growth. As a rule of thumb, divide phlox every two to four years when new growth appears in spring or four to six weeks before the first fall frost so roots have time to develop before the cold arrives. Plants are hardy in Zones 2 to 9. Pictured: Phlox subulata 'Atropurpurea'.

Learn More: Planting and Growing Garden Phlox

Blanket Flower

Butterflies swarm blanket flower when it’s in full bloom, and Gaillardia 'Arizona Red Shades' (pictured) is no exception. This tough perennial withstands drought once established and prefers gritty, lean soils. Remove spent blooms to encourage more flower buds to form. Dig up the plants every two or three years in spring or fall and divide them into sections, each with good roots. Plants are hardy in Zones 3 to 10.

Learn More: Blanket Flower

Monkshood

Lengthen your garden season by including monkshood in your planting areas. This purple-flowered perennial starts opening buds as frost is knocking at the garden gate — and keeps blooming through light frosts. Deer and rabbit dislike monkshood, which is poisonous to people if consumed. Plants can be slow to establish. Divide only when clumps are crowded, which shouldn’t occur before the three-year mark. Plants are hardy in Zones 4 to 8.

Bee Balm

Bumblebees, butterflies, hummingbirds and other pollinators can’t resist the red petals of this bee balm. Monarda didyma 'Jacob Cline' (pictured) boasts excellent resistance to powdery mildew, which typically plagues bee balm in late summer. Snip flowers for bouquets; savor the blooms and leaves in herbal tea. Dig and divide bee balm in early spring every two to three years as soon as new growth emerges. 'Jacob Cline' blooms all season long and is hardy in Zones 4 to 9.

Learn More: Growing Monarda: When to Plant and How to Grow Bee Balm

Tickseed Coreopsis

Tickseed is a native plant, which means it's a snap to grow once it's established. Coreopsis 'Presto' (pictured) improves upon the true native with 2-inch-wide blooms that are semi- or fully double and make terrific additions to bouquets. Dig up the plants and split them with a clean, sharp trowel every two or three years in spring or early fall. Butterflies will definitely visit this perennial, which is hardy in Zones 4 to 9.

Learn More: Common Coreopsis: How to Grow and Care for Coreopsis

Pincushion Flower

Use pincushion flowers to add eye-catching color to bed edges or containers. Give these butterfly-beckoning plants full sun with average soil. Remove spent flowers to extend the bloom period by encouraging more buds to form. Cut the plants back in fall and divide them into clumps every two or three years; you can also divide in early spring. 'Butterfly Blue' (pictured) is hardy in Zones 3 to 9.

Bearded Iris

Give your late spring garden a touch of hybrid beauty with bearded iris. 'Autumn Circus' (pictured) has beautiful purple and white blooms but other varieties offer a range of shades. Site plants in full sun for the strongest flower show and make sure the soil drains well year-round. Fertilize in early spring, after flowers fade, and again in early fall. Divide the rhizomes after the flowers finish, usually from midsummer to early fall. Dig up entire clumps and cut them into smaller sections with a sharp spade or knife. Leave some roots and at least one leaf fan on each section. Trim the leaf fans to 6 to 10 inches tall and replant. 'Autumn Circus' is hardy in Zones 3 to 10.

Learn More: Iris Flower: Varieties to Grow and How to Care for Them

Painted Daisy

Painted Daisy is a cinch to grow. Just give plants full sun and well-drained soil — then get ready for the flower show. Blooms appear in late spring to early summer; remove faded flowers to encourage more to form. This perennial is a rabbit favorite, so take precautions to protect plants with netting or fences. To divide, dig up clumps in spring or fall and cut each one into sections with good roots. Painted Daisy is hardy in Zones 3 to 7. Pictured: Tanacetum 'Robinson’s Red'.

Beardtongue

A hummingbird favorite, beardtongue (penstemon) is a native perennial that thrives in full sun. Plants crave well-drained soil and tolerate drought once established. Beardtongue yields the best results in the garden when used in mass plantings. Let plants mature for three to five years before dividing them in early spring; then cut the roots apart with pruning shears, leaving plenty of roots on each section. Beardtongue is hardy in Zones 3 to 8. Pictured: Penstemon 'Prairie Dusk'.

Tools to Use for Dividing Perennials

Choose a cool, cloudy day to divide and replant. Water the plant thoroughly and let it drain while you gather your tools: sharp blades, whether they come in a pair (pruners) or as single blades like this perennial divider (the large tool) or the big knife (sold as Fiskars Big Grip Knife). A similar tool is the Japanese hori-hori knife.

There are two options for dividing perennials. You can dig up entire clumps and separate them into smaller clumps (the preferred method), or use a sharp shovel to slice down and remove sections of the plant, leaving part of it intact. Sometimes sections will naturally split off.

Keep the sections or clumps in a shady spot while you work with them. If the roots are tangled, use two garden forks to separate them. Cut fleshy roots into sections. Make sure each one has a portion of roots and leaves. Prune away dead or damaged tissue.

Shop: 25 Garden Tools and Essentials for Year-Round Care

How to Plant Perennial Divisions

If you're giving away the divisions, keep them in containers with moist soil around the roots. Water them and keep them in a cool, shady spot. Plant divisions as soon as possible. Set the plants in holes at the same depth they were in the original bed. Water them well and keep them well watered throughout the first year. They'll thrive with cool temperatures and gentle moisture.

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