Plant Division: why, when and which perennials to divide
October 12, 2011In addition to spring, fall is one of the best times to dig, divide, and replant crowded perennials. Signs of stress that a plant is in need of division include:
- Decline in flower performance and size
- Congested clump or overcrowded roots.
- Dead center leaving a hole with growth around the outer edges
Dividing will rejuvenate the parent plant, deliver propagation, and eliminate crowding among plants. It’s best to divide after flowering. Before dividing perennials, decide when (see list below) and where to transplant the seedlings. Consider water output, soil type and drainage, light exposure, and compatibility with new or existing neighboring perennials. Water-loving plants won’t survive in a bed alongside drought plants with little irrigation. Prepare the bed by weeding and adding needed amendments.
If you don’t have room in the landscape for transplants, pot them up for holiday gifts in attractive containers with eye-catching labels detailing plant information.
Divide in fall:
| Name | Special Note |
| Arum (Arum italicum) | |
| Canna (Canna spp.) | |
| Foxtail lilies (Eremurus spp.) | |
| Iris (Iris spp.) | |
| Moss pink (Phlox subulata) | |
| Peonies (Paeonia cvs.) | |
| Poppy (Papaver spp.) | Use root cuttings or dormant plants. |
| Siberian iris (Iris sibirica) | |
| Sweet woodruff (Galium odoratum) |
Plants to divide in spring
| Plant Name | Special Note |
| Anemone (Anemone × hybrida) | |
| Aster (Aster spp.) | Discard old clump |
| Bleeding heart (Dicentra spp.) | After flowering. Every four years sow seeds in fall. |
| Caladium (Caladium spp.) | |
| Calla lily (Zantedeschia aethiopica) | |
| Catmint (Nepeta × faassenii) | Discard old clumps. |
| Dahlia (Dahlia spp.) | Store clumps over winter. |
| Doll’s eyes (Actaea pachypoda) | |
| Delphinium (Delphinium ssp.) | |
| Elephant ear (Alocasia spp.) | |
| Gayfeather (Liatris spicata) | |
| Jacob’s ladder (Polemonium spp.) | Spring or summer |
| Lily-of-the-valley (Convallaria majalis) | Seedlings take several years to flower. Mulch in fall. |
| Primrose (Primula spp.) | |
| Rhubarb (Rheum palmatum) | |
| Wild ginger (Asarum europaeum) |
Divide in spring or early fall:
| Botanical Name | Special Note |
| African lily (Agapanthus cvs.) | |
| Amsonia (Amsonia spp.) | |
| Astilbe (Astilbe spp.) | |
| Bear’s breeches (Acanthus spinosus) | |
| Bee balm (Monarda didyma) | |
| Bellflower (Campanula spp.) | |
| Bergenia (Bergenia cordifolia) | |
| Big bluestem grass (Andropogon gerardii) | |
| Black-eyed Susans (Rudbeckia spp.) | |
| Blanket flower (Gaillardia spp.) | |
| Blood grass (Imperata cylindrica) | |
| Bugleweed (Ajuga reptans) | |
| Cactus | |
| Cardinal flower (Lobelia cardinalis) | |
| Columbine (Aquilegia spp.) | |
| Coneflower (Echinacea purpurea) | |
| Coral bell (Heuchera spp.) | |
| Corydalis (Corydalis lutea) | |
| Cranesbill (Geranium spp.) | |
| Creeping Jenny (Lysimachia nummularia) | |
| Daisy (Leucanthemum × superbum) | |
| Daylily (Hemerocallis spp.) | |
| Deadnettle (Lamium maculatum) | |
| Epimedium (Epimedium spp.) | |
| Foam flower (Tiarella cordifolia) | |
| Forget-me-not (Myosotis sylvatica) | |
| Forest grass (Hakenochloa macra) | |
| Fountain grass (Pennisetum alopecuroides) | |
| Garden phlox (Phlox paniculata) | |
| Gaura (Gaura lindheimeri) | |
| Goatsbeard (Aruncus dioicus) | |
| Goldenrod (Solidago spp.) | |
| Gunnera (Gunnera manicata) | |
| Hosta (Hosta spp.) | |
| Japanese painted fern (Athyrium niponicum ‘Pictum’) | |
| Jerusalem sage (Phlomis russeliana) | |
| Joe Pye weed (Eupatorium maculatum) | |
| Lady’s mantle (Alchemilla mollis) | |
| Lamb’s ear (Stachys byzantina) | |
| Lady fern (Athyrium filix-femina) | |
| Lemon balm (Melissa officinalis) | |
| Ligularia (Ligularia dentata) | |
| Lilyturf (Liriope spicata) | |
| Male fern (Dryopteris filix-mas) | |
| Masterwort (Astrantia major) | |
| Meadowsweets (Filipendula spp.) | |
| Penstemon (Penstemon spp.) | |
| Perennial sage (Salvia × superba) | |
| Pinks (Dianthus plumarius) | |
| Pulmonaria (Pulmonaria spp.) | |
| Pussytoes (Antennaria dioica) | |
| Red hot pokers (Knifophia spp.) | |
| Rodgersia (Rodgersia pinnata) | |
| Sea thrift (Armeria maritima) | |
| Sedge (Carex morrowii) | |
| Silver grasses (Miscanthus spp.) | |
| Snakeroot (Cimicifuga racemosa) | |
| Solomon’s seal (Polygonatum odoratum) | |
| Speedwell (Veronica spicata) | |
| Spurge (Euphorbia myrsinites) | |
| Stonecrop (Sedum spectabile) | |
| Switch grass (Panicum virgatum) | |
| Tickseed (Coreopsis verticillata) | |
| Turtlehead (Chelone glabra) | |
| Violets, pansies (Viola spp.) | |
| Wild indigo (Baptisia australis) | |
| Wormwood (Artemisia ludoviciana) | |
| Yarrow (Achillea millefolium) |
In and Around the Garden 
Help. Divde or discard? I was thinking yesterday about my ‘martha washington geraniums’ in the homemade flowerboxers I have on the carport divider. Seems they’ve reached their ‘peak production’ for the season. I was going to pull them up and throw them in the gardening recycle. Is this the right thing to do?
Also, any suggestions for wintertime plants to replace the ‘martha washingtons’ which gave us lots of delightful color over the spring and summer, with little effort other than a occasional watering.
Thanks Dianne.
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Good Thursday Morning Dianne:
Once again thank you for so much information…I love learning all that you know…LOL
Kisses Kim
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