How and Why to Divide Perennials

Why Divide Perennials?

There are three primary reasons for dividing perennials: to control the size of the plants; to help rejuvenate your plants; and to increase the number of plants you have. This is an inexpensive way to gain additional plants for your garden (or to share with others).

When Should You Divide Perennials?

This depends on whether your plants bloom in the spring or the fall. It is best to divide your fall-blooming plants in the spring, and vice-versa for those that bloom in the spring.

If you do this in the spring, it should be done as soon as the growing tips emerge in early spring. You need to allow enough time for the roots to develop before the hot weather of summer arrives.

Most perennials should be divided every three to five years. Some such as chrysanthemums and asters may need to be done every one to two years or they will crowd themselves into non- flowering clumps of leaves and roots.  Unless you want to increase your numbers, bleeding hearts and peonies don’t need dividing at all.

Don’t wait until a plant has become decrepit or monstrous to divide it. The rule of thumb is when it looks its best, divide it at the end of that year. Watch for the early signs of trouble: when the center of the plant has smaller leaves, fewer flowers, and weaker blooming stalks than the outer edges like this Sedum ‘Autumn Joy’, or when the plant runs out of growing room on its edges and has nowhere to go but into neighboring plants.

perennial div.

How to Divide Perennials

Use a sharp pointed trowel or shovel (or spading fork) to dig down deep on all four sides of the plant, about 4 to 6 inches away from the plant. Pry underneath  with your tool and lift the whole clump to be divided.

Depending on the the root system, there are different ways to separate:

  • Spreading root system-This is most common for such plants as asters, lamb’s ear, and cornflowers. They can usually be pulled apart by hand, or cut with a knife, but may need more forceful separation using digging forks to pry the roots apart.
  • Clumping root system-This group includes astilbes, hostas, daylillies, and ornamental grasses. It is often necessary to cut through the fleshy crowns with a heavy sharp knife. Keep at least one or more developing eye or bud with each division. If you want bigger plants, keep several eyes.
  • Rhizomes- These are stems that grow horizontally near the surface. Bearded irises are the most common with this type of system. Divide these any time from a month after flowering until the fall.
  • Tuberous Roots-Dahlias are this type of perennial.  The tubers should be cut apart with a knife. Every piece must have a piece of the original stem and a growth bud attached. Replant after dividing. Never allow the divisions to dry out.

For more information about specific plants and when and how to divide, go to