Toronto Master Gardener Factsheet    

Why divide

• To get more plants or to keep plants from overcrowding
• To keep perennials fresh and young. Plants that make new growth around the periphery tend to die out in the centre with age.

When to divide

• Dividing can be done in Spring and Fall
• Spring dividing should be done when a couple of inches of growth are showing. Make sure the plant is well watered before you begin.
• It is best done when the weather is cool and the ground moist. The ideal day is overcast so that the roots don't dry out quickly.
• Late bloomers such as chrysanthemums and asters should be divided in spring because there is not enough time to re-establish after bloom in fall. Perennials that bloom in April and May such as primula should be left until after they bloom.
• Fall dividing should be done early so that the roots have time to establish before winter.

How to divide

• To divide a clump-forming plant, lift the whole plant by digging up as much of the root ball as possible. Shake or tease off enough soil from the roots so that you can see the roots and crown. Pull the clump apart into root pieces with several growing points on each section.
• For plants that grow by runners or spreading roots, dig up new, extra roots only and move to another location.

Replanting

• Choose the strongest parts from the outside of the plant and replant a few pieces to replace the original clump. The extra pieces can be planted in new areas or potted up to give away. (Use plastic bags and wet newspaper around the roots if only holding for a few days.)
• Add compost or well-rotted manure to enrich the soil. Mix with excavated soil.
• Plant at same level in newly prepared hole. Tamp the soil firmly around the plant.
• Water immediately and keep watered for the next few weeks to help it survive the shock.
• Discard (compost) the woody centre of the old plant.

Hints for dividing

• Hosta and daylilies (hemerocallis) are sometimes difficult to separate into pieces. Try working with two garden forks, back to back, and pry apart. If necessary, use a large knife or split with a spade.
• Some plants dislike moving or division, such as oriental poppies (a long tap root), peonies, gypsophila (baby's breath) and euphorbia. But if they are not doing well where they are, you might as well take a chance!

Factsheets are produced by the Toronto Master Gardeners in association with the Toronto Botanical Garden. They provide introductory information about a broad range of horticultural topics and are intended for personal use and study purposes. Should your gardening group or organization wish to use multiple copies we ask that you inform the Toronto Botanical Garden at info@torontobotanicalgarden.ca.

Date revised: This factsheet was created prior to May 2005.