Dividing Perennials

Milorganite Flowers Dividing Perennials

Quick Tips

  • Best time to divide perennials is in the fall
  • Perennials are healthiest when they have room to spread
  • Dig the entire plant out or simply take out slices

Perennial plants are healthiest when they are young and have room to spread. After several seasons of growing perennials they will begin to die out in the center or simply cease flowering. To keep these plants actively growing and healthy, a technique known as 'Division' is performed.

Why divide perennials?

  • The bed is over crowded
  • Centers of the plants are dying out
  • The plants are no longer flowering
  • Increase the number of plants

 

How to divide a perennial:

  • Cut back the foliage and dig the entire plant out of the ground or just simply take out slices of the plant. Look for natural sections to pull apart, or use a knife or saw to cut into pieces. Plant in new location and be sure to fertilize and water.
  • Typically, the best time of the year to divide is in the fall.
  • In cold-winter areas, stop fertilizing perennials by midsummer to encourage them to slow their growth and harden off for winter.
  • In warm-winter areas, fall is a good time to plant perennials. However, in winter check for signs of disease, especially during wet periods, since the plants are growing slowly and conditions are right for rotting to occur.

 

Below is a list of some of the most common perennial varieties and the appropriate time to divide these species for the best results.  For more information on dividing perennials, watch Garden Gate Magazine's video or download PDF chart of plants with specific tips for dividing each.

Dividing Perennials Chart
Plant Name Tips for Dividing
Aster Divide every 2 or 3 years in spring
Astilbe Divide every 3 or 4 years in spring.
Baby’s Breath Division is difficult; carefully divide in spring or late summer/early fall.
Basket-of-Gold Divide in late summer/early fall. Basket-of-gold also can be propagated by stem cuttings in spring or late summer.
Bee Balm Divide approximately every third year in spring.
Blanket Flower Divide in spring.
Blazing Star Divide in spring.
Bleeding Heart Best done in late summer/early fall. Also can be divided in spring.
Butterfly Weed A taproot makes division difficult. However, butterfly weed is easily propagated by seeds.
Chrysanthemum Divide mums every 2 or 3 years in spring.
Columbine Many species and varieties are short-lived. Division is difficult, carefully divide in late summer.
Coral Bells Divide in spring or late summer/early fall.
Coreopsis Divide in spring or late summer/early fall.
Cornflower Requires division every 2 or 3 years. Divide in spring.
Daylily Divide in spring or late summer/early fall.
Delphinium Usually short-lived, division is seldom necessary.
False Indigo Division is difficult because of its long taproot. Plants can be started from seeds.
Gooseneck Loosestrife Plants spread aggressively. Divide every 2 or 3 years in spring.
Hardy Geranium Divide in spring or late summer/early fall.
Hardy Zinnia 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 Divide every 3 to 4 years in July or August.
Iris, Siberian Divide after blooming in early summer.
Lily-of-the-Valley A rapidly spreading groundcover, divide in spring.
Lungwort Divide in late summer/early fall.
Obedient Plant Plants spread rapidly. Divide plants every 2 or 3 years in spring.
Oriental Poppy Divide when plants die back in mid- to late summer.
Orange Coneflower Divide every 3 or 4 years in spring.
Ornamental Grasses Spring is the best time to divide ornamental grasses. Also can be divided in late summer/early fall.
Peony Peonies are long-lived and can be left undisturbed for many years. If additional plants are desired, divide clumps in September.
Perennial Salvia Divide plants in spring.
Phlox, Garden Divide every 3 to 4 years
Phlox, Moss Divide plants in spring immediately after blooming.
Purple Coneflower Divide every 3 to 4 years in spring.
Shasta Daisy Divide in spring.
Speedwell Divide in spring or late summer / early fall.
Yarrow Divide every 2 to 3 years in spring.

*List courtesy of Iowa State University Extension "When to Divide Perennials" publication, September 2006.