Perennials can often be divided to control size, retain vigor and to share with a friend. Other perennials decline if not divided every few years at the appropriate time. One of the easiest ways to propagate your prized perennials is to divide the plant into two or more. To divide a perennial, either cut down into the clump with a sharp spade and lift out the separate chunks, or dig up the entire plant and pry it apart by hand

Division Instructions per Species

Aster
Divide every 2-3 years in spring

Astilbe
Divide every 3-4 years in spring

Baby’s Breath (Gypsophila) 
Division is difficult, carefully divide in spring or late summer/early fall

Basket-of-Gold (Aurinia)
Divide in late summer/early fall.

Bee Balm (Monarda)
Divide approx. every third year in spring

Blanket Flower (Gaillardia)
Divide in spring

Blazing Star (Liatris)
Divide in spring

Bleeding Heart (Dicentra)
Division is difficult, best done in late summer/early fall

Butterfly Weed (Asclepias)
A taproot makes division difficult.  Easily propagated by seeds

Chrysanthemum
Divide every 2-3 years in spring

Columbine (Aquilegia)
Many species and varieties are short lived. Division is difficult, carefully divide in late summer

Coral Bells (Heuchera)
Divide in spring or late summer/early fall

Tickseed (Coreopsis)
Divide in spring or late summer/early fall

Cornflower (Centaurea)
Requires division every 2-3 years.  Divide in spring.

Daylily (Hemerocallis)
Divide in spring or late summer/early fall

Delphinium
Usually short-lived , division is seldom necessary

False Indigo (Baptisia)
Division is difficult because of its long taproot.  Plants can be started from seed

Gooseneck Loosestrife (Lysimachia clethroides)
Plants spread aggressively.  Divide every 2-3 years in spring

Hardy Geranium (Geranium)
Divide in spring or late summer/early fall

Ox Eye (Heliopsis)
Divide every other year in spring or late summer/early fall

Hosta
Plants can be left undisturbed for years.  If additional plants are desired, divide clumps in spring or late summer/early fall

Iris, Bearded (Iris germanica)
Divide every 3-4 years in July or August

Iris, Siberian (Iris sibirica)
Divide after blooming in early summer

Lily of the Valley (Convallaria)
A rapidly spreading groundcover, divide in spring

Lungwort (Pulmonaria)
Divide in late summer/early fall

Obedient Plant (Physostegia)
Plants spread rapidly.  Divide plants every 2-3 years in spring

Oriental Poppy (Papaver)
Divide when plants die back in mid to late summer

Ornamental Grass
The best time is spring. Also can be divided in late summer/early fall

Peony (Paeonia)
Peonies are long-lived and can be left undisturbed for years.  If additional plants are desired, divide clumps in September

Perennial Salvia (Salvia)
Divide plants in spring

Phlox, Garden (Phlox paniculata)
Divide every 3-4 years in spring or late summer/early fall

Phlox, Moss (Phlox subulata)
Divide plants in spring immediately after blooming

Purple Coneflower (Echinacea)
Divide every 3-4 years in spring

Shasta Daisy (Leucanthemum)
Tends to be short-lived.  Divide plants in spring

Speedwell (Veronica)
Divide in spring or late summer/early fall

Spiderwort (Tradescantia)
Divide every 2-3 years in spring

Stonecrop (Sedum)
Divide in spring

Yarrow (Achillea)
Many of the Yarrows spread rapidly.  Divide every 3-4 years in spring