Dividing Perennials

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Quick Tips:

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

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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.

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.