Timing is important

Timing is important

by Todd Meier

When dividing perennials, timing and technique are important. And while many perennials can be divided in either early spring or early fall, some are very picky. The optimal time to divide specific perennials is denoted by (S) for spring and (F) for early fall. A single asterisk indicates that division should take place after the plant flowers. Two asterisks mean that protective gloves should be worn when dividing the plant, since its sap may irritate skin.

Divide these plants by hand
Blanket flowers (Gaillardiaspp.) S/F
Bleeding hearts (Dicentraspp.) S*
Bugleweed (Ajuga reptans) S/F
Columbines (Aquilegiaspp.) S/F
Coral bells (Heucheraspp.) S/F
Cranesbills (Geraniumspp.) S/F
Creeping Jenny (Lysimachia nummularia) S/F
Deadnettle (Lamium maculatum) S/F
Epimediums (Epimediumspp.) S*/F
Foam flower (Tiarella cordifolia) S/F
Forget-me-not (Myosotis sylvatica) S*/F
Hellebores (Helleborusspp.) S*/F
Jacob’s ladder (Polemonium caeruleum) S/F
Lady’s mantle (Alchemilla mollis) S/F
Lamb’s ears (Stachys byzantina) S/F
Moss pink (Phlox subulata) F
Primroses (Primulaspp.) S*
Pulmonarias (Pulmonariaspp.) S*/F
Pussytoes (Antennaria dioica) S/F
Sea thrift (Armeria maritima) S/F
Speedwell (Veronica spicata) S/F
Spurge (Euphorbia myrsinites) S/F**
Stonecrop (Sedum spectabile) S/F
Sweet woodruff (Galium odoratum) F
Violets, pansies (Violaspp.) S/F
Wormwood (Artemisia ludoviciana) S/F
Yarrow (Achillea millefolium) S/F

Divide these plants with a spade or pitchfork
African lilies (Agapanthuscvs.) S/F
Anemone (Anemone × hybrida) S
Asters (Asterspp.) S
Bee balm (Monarda didyma) S/F
Bellflowers (Campanulaspp.) S/F
Big bluestem grass (Andropogon gerardii) S/F
Black-eyed Susans (Rudbeckiaspp.) S/F
Blood grass (Imperata cylindrica) S/F
Cardinal flower (Lobelia cardinalis) S/F
Catmint (Nepeta × faassenii) S/F
Coneflower (Echinacea purpurea) S/F
Daisy (Leucanthemum × superbum) S/F
Daylilies (Hemerocallisspp.) S/F
Forest grass (Hakenochloa macra) S/F
Fountain grass (Pennisetum alopecuroides) S/F
Garden phlox (Phlox paniculata) S/F
Gaura (Gaura lindheimeri) S/F
Goldenrods (Solidagospp.) S/F
Gunnera (Gunnera manicata) S/F
Hostas (Hostaspp.) S/F
Japanese painted fern (Athyrium niponicum‘Pictum’) S/F
Jerusalem sage (Phlomis russeliana) S/F
Lemon balm (Melissa officinalis)
Ligularia (Ligularia dentata) S/F
Masterwort (Astrantia major) S/F
Monkshood (Aconitum napellus) S
Penstemons (Penstemonspp.) S/F
Perennial sage (Salvia × superba) S*/F
Pinks (Dianthus plumarius) S/F
Poppies (Papaverspp.) F
Red hot pokers (Knifophiaspp.) S/F
Sedge (Carex morrowii) S/F
Siberian iris (Iris sibirica) F
Silver grasses (Miscanthusspp.) S/F
Snakeroot (Cimicifuga racemosa) S/F
Switch grass (Panicum virgatum) S/F
Tickseed (Coreopsis verticillata) S/F
Turtlehead (Chelone glabra) S/F
Yarrow (Achillea filipendulina) S/F

Slice apart woody crowns with a handsaw
Amsonias (Amsoniaspp.) S/F
Astilbes (Astilbespp.) S/F
Bear’s breeches (Acanthus spinosus) S/F
Doll’s eyes (Actaea pachypoda) S
Foxtail lilies (Eremurusspp.) F
Gayfeather (Liatris spicata) S/F
Goatsbeard (Aruncus dioicus) S/F
Joe Pye weed (Eupatorium maculatum) S/F
Lilyturf (Liriope spicata) S/F
Male fern (Dryopteris filix-mas) S/F
Meadowsweets (Filipendulaspp.) S/F
Peonies (Paeoniacvs.) F
Solomon’s seal (Polygonatum odoratum) S/F
Wild indigo (Baptisia australis) S*/F

Cut up rhizomes and tubers with a knife
Arum (Arum italicum) F
Bergenia (Bergenia cordifolia) S/F
Caladiums (Caladiumspp.) S
Calla lily (Zantedeschia aethiopica) S
Cannas (Cannaspp.) S
Corydalis (Corydalis lutea) S/F
Dahlias (Dahliacvs.) S
Elephant ears (Alocasiaspp.) S
Irises (Irisspp.) F
Lady fern (Athyrium filix-femina) S/F
Lily-of-the-valley (Convallaria majalis) S/F
Rhubarb (Rheum palmatum) S
Rodgersia (Rodgersia pinnata) S/F
Spurge (Euphorbia griffithii) S/F**
Wild ginger (Asarum europaeum) S

These perennials are best not divided
Alyssums (Alyssumspp.)
Candytuft (Iberis sempervirens)
Carnation (Dianthus caryophyllus)
Delphinium (Delphinium × elatum)
Euphorbia (Euphorbia characiasssp. wulfenii)
Foxgloves (Digitalisspp.)
Garden sage (Salvia officinalis)
Geraniums (Pelargoniumspp.)
Lavender cotton (Santolina chamaecyparissus)
Lavenders (Lavandulaspp.)
Rose campion (Lychnis coronaria)
Rosemary (Rosmarinus officinalis)
Russian sage (Perovskia atriplicifolia)
Sea hollies (Eryngiumspp.)
Silvermound (Artemisia schmidtiana)
Sweet pea (Lathyrus latifolius)
Trillium (Trillium grandiflorum)