Division is one of the easiest ways to propagate perennials. It’s also a life-saving measure for some plants that need to be divided periodically for the health of the plant. (Irises, coreopses and Shasta daisies will eventually die if they're never divided).
This is what I learned about dividing plants at The New York Botanical Garden:
- Lift the plant completely out of the ground. This will enable you to gently divide it at the root ball level rather than cut through the crown from the top with your spade. Cutting through the crown will damage roots, causing the plant to take longer to recover.
Lifting a Shasta daisy out of the ground for dividing
- After lifting the plant from the ground, lay it on its side and spear the side of the root ball with a long-handled fork facing outward from the center. Place a second fork into the root ball facing the other way, letting the tines line up next to one another. Step on the fork with your foot if you need to use force to thrust the tines down into the root ball.
- Once the forks are firmly in the root ball, gently pull the two handles away from each other. This will cause the roots to separate into two clumps. The roots can then be teased apart with minimal damage.
- Replant the two clumps and insulate against the cold to come. The best way to insulate newly planted perennials is to cover them with evergreen boughs after the ground has frozen. This helps prevent the ground from thawing and then freezing, which can cause plants to heave out of the ground. (See “The Curious Gardener,” January 2012.)
When to Divide
Fall is a great time to divide most plants, especially late-spring and summer-blooming perennials, from peonies to daylilies to daisies. Some exceptions are early-spring bloomers which should be divided just after they bloom so they have all season to prepare for next season. Bearded irises should be divided mid-July to mid-August, or they won’t bloom the following season. Ornamental grasses should never be divided in the fall. Wait until they start to show growth in the spring, and then try dividing them.
How to Divide Bearded Irises
Bearded irises have rhizomes. A rhizome is a continuously growing underground stem that puts out lateral shoots and roots. Dig the plant out of your garden bed and drop it to the ground. See where it naturally breaks, and then make clean cuts with a sharp knife. Cut out any rotted pieces. Cut the foliage back to 3 to 5 inches from the rhizome and replant.
Do Daffodils Need to Be Divided?
Daffodils do not need to be divided, but they should be fed every few years in the fall.
Dorian Winslow is the president of Womanswork, and is passionate about making the best products on the market for women who garden and work outdoors.