One of the easiest ways to propagate a prized perennial is to divide the plant into two or more smaller plants. Below are tips and recommendations for dividing perennials in your garden including information on why, how, when, and how frequently to divide. Included are guidelines for specific perennial species common in Iowa gardens.
Why Divide? | How to Divide | When to Divide | How Often to Divide | Guidelines for Specific Species | FAQs | More Information
Why Divide Perennials?
As perennials grow in the garden, they often benefit from division. There are many reasons why division can be beneficial.
Some Perennials Need Rejuvenation
The performance of some perennials, such as bearded iris (Iris hybrids), begins to decline after several years. If not divided every 3 to 5 years, some species will not bloom well because of overcrowding. Declining perennials should be divided to rejuvenate the plants.
Some Perennials are Vigorous Growers
Other perennials need to be divided periodically to contain their spread. Vigorous growing perennials such as gooseneck loosestrife (Lysimachia clethroides) or obedient plant (Physostegia virginiana) grow so rapidly that they begin to crowd out neighboring plants within a few years. Vigorous growers should be divided every 2 to 3 years. After dividing the perennials, replant some of the divisions, give others to relatives or neighbors, and discard the remaining plants in the compost pile.
Some Perennials Die-out in the Center
Some clump-forming perennials like hosta (Hosta sp.) and many ornamental grasses like maiden grass (Miscanthus sinensis) will develop dead centers in their crowns as they age. Over time these plants will get large enough that the dead area in the middle will be obvious and unattractive. Divide these species when you notice a dead spot forming in the center. Be sure to discard the dead portions of the clump when breaking or cutting the root system apart.
Sometimes We Want More Plants
One of the great benefits of propagation of any kind, including division, is that you get more plants (and who doesn't want more plants?!). Division helps create new plants that are healthy and ready to grow allowing you to fill in empty spaces, start new perennials borders, and share with friends and neighbors.
Not All Perennials Need Regular Division
Some perennials, such as garden peonies (Peonia sp.), can be left undisturbed for 50 or more years. Species that do not grow vigorously, easily spread, or require rejuvenation do not need to be divided frequently.
While most perennials are easy to divide, a few perennial species, like butterfly weed (Asclepias tuberosa) and false blue indigo (Baptisia australis) are difficult to divide because of deep taproots or extensive root systems. These perennials prefer to be left undisturbed. These species are best propagated with other methods such as seed.
How to Divide Perennials
Spring Division
In Iowa, many perennials are best divided in early spring just as the foliage is emerging from the ground (April). Division at this time makes it easy to see where the root ball is located allowing you to easily dig up the entire plant. Additionally, because the foliage is small, it does not get in the way of splitting the plants.
- Start by digging the entire plant out of the ground making sure to get the entire root ball up out of the hole.
- Separate the plant clump into sections with a sharp knife or spade. Each division should contain several shoots and a portion of the root system.
- Species requiring careful handling can be gently teased apart with your hands.
- The larger each section is, the quicker the new plant will become established and look nice.
- Smaller sections may take a little more time to recover but allow you to have more propagules.
Some perennials are best separated into smaller pieces with a knife or sharp spade. - Replant the divisions immediately.
- Place the divisions at the same level in the ground as they were growing previously.
- If the divisions cannot be planted in their new location right away, place the plants temporarily in a container and hold the plants in a protected shade to part-shade location. Water when the root ball is dry. The sooner the plants can be planted in their permanent location, the better.
- Apply a layer of mulch to help conserve soil moisture and reduce weed growth.
- Keep the newly divided perennials well-watered through spring and summer.
Most newly divided perennials do not bloom well until their second growing season.
Fall Division
Late summer/early fall (mid-August through September) is a good time to divide some perennials in Iowa. Allow at least 4 to 6 weeks before the ground freezes for the plants to become established.
Follow the same procedure for division in late summer as you would for division in the spring.
Most perennials divided later in the growing season should be mulched in November. A 4 to 6-inch layer of straw placed over the plants should reduce the possibility of winter injury. Remove the mulch in early April.
When to Divide Perennials
The best time to divide perennials varies with the different plant species. Early spring (just as new growth begins to appear) is the best time to divide many species. Other species can be divided in late summer/fall (mid-August through September). Consult the table below to determine the best timing for your perennial.
How Often to Divide Perennials
The frequency of dividing perennials can vary depending on the species. Many factors will determine when to split perennials. Vigorous growers should be divided every 2 to 3 years. Those perennials that see reduced flowering as they age benefit from division every 3 to 5 years to rejuvenate them. Those species that die out in the center may be able to go longer than 7 or 8 years before the dead center becomes noticeable. As long as plants are large and healthy enough to split into smaller pieces, they can be divided, whether that is every 2 years or every 20 years.
Season and Frequency of Division by Species
| Plant | When to Divide |
|---|---|
| Aster (Aster spp.) | divide every 2 or 3 years in spring. |
| Astilbe (Astilbe spp.) | divide every 3 or 4 years in spring. |
| Baby's Breath (Gypsophila paniculata) | division is difficult, carefully divide in spring or late summer/fall. |
| Balloon Flower (Platycodon grandiflorus) | division is difficult because of its long taproot, carefully divide in spring |
| Barren Strawberry | divide in spring or late summer/fall. |
| Basket-of-Gold (Aurinia saxatilis) | divide in late summer/fall. Basket-of-gold can also be propagated by stem cuttings in spring or fall. |
| Beardtongue (Penstemon spp.) | divide in spring |
| Bee Balm (Monarda didyma) | divide approximately every third year in spring. |
| Bellflower (Campanula spp.) | divide in spring or late summer/fall. |
| Black-eyed Susan (Rudbeckia hirta) | divide every 3 or 4 years in spring. |
| Blanket Flower (Gaillardia x grandiflora) | divide in spring. |
| Blazing Star (Liatris spp.) | divide in spring. |
| Bleeding Heart (Lamprocapnos spectabilis) | division is difficult, best done in late summer/fall. |
| Bugle Weed (Ajuga reptans) | divide in spring or late summer/fall. |
| Burnet (Sanguisorba obtusa) | divide in spring or late summer. |
| Butterfly Weed (Asclepias tuberosa) | a taproot makes division difficult. However, butterfly weed is easily propagated by seeds. |
| Candytuft (Iberis sempervirens) | divide in spring or late summer/fall. |
| Cardinal Flower (Lobelia cardinalis) | divide in spring or late summer/fall. |
| Catmint (Nepeta spp.) | divide in spring or immediately after first bloom. |
| Carolina Lupine (Thermopsis villosa) | division is difficult due to deep roots and slow re-establishment, carefully divide in early spring. |
| Chrysanthemum (Chrysanthemum ×grandiflorum) | divide mums every 2 or 3 years in spring. |
| Columbine (Aquilegia spp.) | many species and varieties are short-lived. Division is difficult, carefully divide in late summer. |
| Coral Bells (Heuchera spp.) | divide in spring or late summer/fall. |
| Coreopsis (Coreopsis spp.) | divide in spring or late summer/fall. |
| Cornflower (Centaurea spp.) | requires frequent division every 2 or 3 years. Divide in spring. |
| Daylily (Hemerocallis spp.) | divide in spring or late summer/fall. |
| Delphinium (Delphinium spp.) | usually short-lived, division is seldom necessary. |
| False Forget-Me-Not (Brunnera macrophylla | divide in spring or late summer/fall. |
| False Indigo (Baptisia australis) | division is difficult because of its long taproot. Plants can be started from seeds. |
| False Sunflower (Heliopsis helianthoides) | divide every other year in spring or late summer/fall. |
| Ferns | divide in spring |
| Foam Flower (Tiarella spp.) | divide in spring or late summer/fall. |
| Gas Plant (Dictamnus albus) | division is difficult, plants are best left undisturbed. Start new plants from seeds. |
| Globe Flower (Trollius spp.) | divide in late summer/fall. |
| Globe Thistle (Echinops ritro) | division is difficult, slow to re-establish,. Carefully divide in spring. |
| Goat’s Beard (Aruncus dioicus) | division is difficult, root system is large and difficult to separate. Carefully divide in early spring. |
| Goldenrod (Solidago spp.) | divide in spring or late summer/fall. |
| Gooseneck Loosestrife (Lysimachia clethroides) | plants spread aggressively. Divide every 2 or 3 years in spring. |
| Hardy Geranium (Geranium spp.) | divide in spring or late summer/fall. |
| Hibiscus, Hardy (Hibiscus moscheutos) | divide rarely in spring or early summer/fall. |
| Hosta (Hosta spp.) | plants can be left undisturbed for years. If additional plants are desired, divide clumps in spring or late summer/fall. |
| Iris, Bearded (Iris hybrids) | divide every 3 to 4 years in July or August. |
| Iris, Siberian (Iris sibirica) | divide after blooming in early summer. |
| Jacob's Ladder (Polemonium caeruleum) | carefully divide in spring. |
| Joe-Pye Weed (Eutrochium purpureum) | divide in spring or late summer/fall. |
| Lady's Mantle (Alchemilla mollis) | rarely needs division. Divide in spring or late summer. |
| Lamb's Ear (Stachys byzantina) | divide in spring or late summer/fall. |
| Lenten Rose (Helleborus orientalis) | divide immediately after flowering in spring. |
| Ligularia (Ligularia spp.) | divide in spring or late summer/fall. |
| Lily (Lilium) | divide in late summer/fall. |
| Lily-of-the-Valley (Convallaria majalis) | a rapidly spreading groundcover, divide in spring. |
| Lungwort (Pulmonaria species) | divide in late summer/fall. |
| Meadow Rue (Thalictrum aquilegifolium) | divisions are slow to re-establish. Divide in spring. |
| Meadowsweet (Filipendula spp.) | divide plants in spring. |
| Milkweed, swamp (rose) (Asclepias incarnata) | a taproot makes division difficult. However, milkweed is easily propagated by seeds. |
| Mint (Mentha spp.) | divide often to control spread in spring or late summer/fall. |
| Monkshood (Aconitum spp.) | division is difficult, plants are slow to re-establish. carefully divide in early spring. |
| Obedient Plant (Physostegia virginiana) | plants spread rapidly. Divide plants every 2 or 3 years in spring. |
| Oriental Poppy (Papaver orientale) | divide when plants die back in mid to late summer. |
| Orange Coneflower (Rudbeckia fulgida) | divide every 3 or 4 years in spring. |
| Ornamental Grasses | the best time to divide ornamental grasses is spring. Can also be divided in late summer/fall. |
| Ornamental Onion (Allium spp.) | divide plants frequently in late summer/fall. |
| Peony (Paeonia hybrids) | peonies are long-lived and can be left undisturbed for many years. If additional plants are desired, divide clumps in September. |
| Perennial Salvia (Salvia hybrids) | divide plants in spring. |
| Phlox, Garden (Phlox paniculata) | divide every 3 to 4 years in spring or late summer/fall. |
| Phlox, Moss (Phlox subulata) | divide plants in spring immediately after blooming. |
| Pigsqueak (Bergenia cordifolia) | divide in spring or late summer/fall. |
| Pincushion Flower (Scabiosa spp.) | divisions are slow to re-establish. Carefully divide in spring. |
| Prairie Smoke (Geum spp.) | divide immediately after flowering in spring or late summer |
| Purple Coneflower (Echinacea purpurea) | divide every 3 or 4 years in spring. |
| Russian Sage (Salvia yangii syn. Perovskia atriplicifolia) | difficult to divide. carefully divide in spring or late summer/early fall. |
| Sea Pink (Armeria maritima) | divide in spring. |
| Sedge (Carex spp.) | divide in spring. |
| Shasta Daisy (Leucanthemum x superbum) | tends to be short-lived. Divide plants in spring. |
| Sneezeweed (Heleniium autumnale) | divide in spring or late summer/fall. |
| Snow-in-summer (Cerastium tomentosum) | divide in spring or late summer/fall. |
| Speedwell (Veronica spp.) | divide in spring or late summer/fall. |
| Spiderwort (Tradescantia spp.) | divide in spring or late summer/fall. Spiderworts are rapidly spreading plants. Divide every 2 or 3 years in spring. |
| Spurge, Cushion (Euphorbia polychroma) | carefully divide in spring or late summer/early fall. |
| Stonecrop (Sedum spp.) | divide in spring. |
| Sundrops (Oenothera spp.) | difficult to divide. Carefully divide in spring or late summer/fall. |
| Toad Lily (Tricyrtis hirta) | divide in spring. |
| Trillium (Trillium spp.) | difficult to divide. Carefully divide in spring. |
| Turtlehead (Chelone spp.) | divide in spring. |
| Wormwood (Artemisia spp.) | divide frequently in spring. |
| Yarrow (Achillea spp.) | many of the yarrows spread rapidly. Divide every 3 or 4 years in spring. |
| Yucca, Adam's Needle (Yucca filamentosa) | difficult to divide because of deep coarse roots. Divide in spring. |
FAQs
- Do I need to divide the perennials in my garden?
- When should I divide my perennials?
- How often can I divide perennials?
- How do I go about dividing perennials in spring?
- Which perennials can be divided in late summer?
- When is the best time to divide asters?
- When is the best time to divide bee balm?
- Can the butterfly weed be divided?
- When is the best time to divide chrysanthemums?
- When can I divide daylilies?
- When is the best time to divide hostas?
- When and how do you divide bearded irises?
- When would be a good time to dig and divide lilies?
- When can I divide lungworts?
- What is the proper way to divide peonies?
- When can I divide garden phlox?
- When would be the best time to divide 'Autumn Joy' sedum?