Dividing Perennials in Fall

Many perennials can be divided to rejuvenate overgrown or decrepit plants, or to create new plants.  Lifting and dividing plants is the perfect time to also replenish the soil with organic matter to encourage healthy growth and prevent disease.

One of the keys to successful division is knowing when to divide what.  Most perennials can be divided at any time, provided they receive adequate care afterward.  However, some prefer to be divided in spring or fall, while other perennials simply don’t respond well to division and are best left alone.

To help you achieve success with all of your plant divisions, here is a list of common perennials, along with when they should, or shouldn’t, be divided.

Divide these plants only in Fall

Arum (Arum italicum)
Foxtail lilies (Eremurus spp.)
Irises (Iris spp.)
Moss pink (Phlox subulata)
Peonies (Paeonia cvs.)
Poppies (Papaver spp.)
Siberian iris (Iris sibirica)
Sweet woodruff (Galium odoratum)

Do not divide these plants in Fall (divide them in the Spring)

Anemone (Anemone × hybrid)
Asters (Aster spp.)
Bleeding hearts (Dicentra spp.)
Monkshood (Aconitum napellus)
Wild ginger (Asarum europaeum)
Primroses (Primula spp.)
Rhubarb (Rheum palmatum)

These perennials are best not divided

Candytuft (Iberis sempervirens)
Carnation (Dianthus caryophyllus)
Delphinium (Delphinium × elatum)
Euphorbia (Euphorbia characias ssp. wulfenii)
Foxgloves (Digitalis spp.)
Garden sage (Salvia officinalis)
Geraniums (Pelargonium spp.)
Lavender cotton (Santolina chamaecyparissus)
Lavenders (Lavandula spp.)
Rose campion (Lychnis coronaria)
Rosemary (Rosmarinus officinalis)
Russian sage (Perovskia atriplicifolia)
Sea hollies (Eryngium spp.)
Silvermound (Artemisia schmidtiana)
Trillium (Trillium grandiflorum)

Division facts

● Divide while the plant still looks beautiful—don’t wait until the center has died out or the plant is overgrown.

● Plant smaller divisions– perennials grow  quickly, as much as tripling in size in just one year.

● Spread the roots out horizontally when planting divisions—this means digging a wide planting hole.