Many, but not all, perennials benefit from division after they have grown for a number of years. This gardening guide describes the common gardening practice of perennial division, including why, when and how to divide your plants. You can replant your divisions, or share or trade them with friends and neighbours, and watch your garden grow!
The main reasons to divide perennials are:
- To get more plants or to keep plants from overcrowding.
- To keep perennials fresh and young. Many perennials make new growth around the periphery and tend to die out in the centre with age.
When to divide
Perennials can be divided in the spring or the fall. 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.
Dividing perennials 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. Make sure the plant is well watered before you begin. Spring dividing should be done when a couple of inches of growth are showing. 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.
For clump-forming perennials, choose the strongest parts from the outside of the plant and replant a few pieces to replace the original plant. The extra pieces can be planted in new areas or potted up to give away. Keep newly-potted plants in the shade – they are already stressed enough. (Use plastic bags and wet newspaper around the roots if only holding for a few days.)
Plant the divisions at same level they had been growing at in the newly prepared hole. Gently push the soil around the roots so that all the roots have contact with the soil. You do not want to compact the soil to be so compacted around the roots to affect soil texture. Pour water over the area so that the soil settles and reduces any large air pockets that might still be present. Water immediately and keep watered for the next few weeks to help it survive the shock. Discard or compost the woody centre of the old plant. Use mulch to insulate newly divided perennials to help retain moisture and protect against fluctuating temperatures.
Hints for dividing
Hostas, daylilies (Hemerocallis) and ornamental grasses 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.
Be careful when buying daylilies. Most hybridized daylilies are well contained in gardens and require division every few years. However, one daylily species Hemerocallis fulva, also sometimes referred to as “ditch lilies” are invasive and capable of displacing native vegetation once established.
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!
How and when to divide perennials : https://extension.umn.edu/planting-and-growing-guides/dividing-perennials
Dividing Perennials : https://hgic.clemson.edu/factsheet/dividing-perennials/
Dividing Perennials: http://chemung.cce.cornell.edu/resources/dividing-perennials
Date revised: September 2021
Prepared by the Toronto Master Gardeners, these Gardening Guides provide introductory information on a variety of gardening topics. Toronto Master Gardeners are part of a large, international volunteer community committed to providing the public with horticultural information, education and inspiration. Our goal is to help Toronto residents use safe, effective, proven and sustainable horticultural practices to create gardens, landscapes and communities that are both vibrant and healthy.
Statement on Invasive Plants: When choosing plants, avoid invasive plants, which can spread quickly and dominate gardens. Invasive plants are sold by nurseries, big box stores or even at community plant sales. Invasives may already be present in your garden. They can invade gardens by spreading from under a neighbour’s fence or may be transported by wildlife. For beautiful, sustainable options to invasive plants, see the Ontario Invasive Plant Council’s “Grow Me Instead – Beautiful Non-Invasive Plants for your Garden” at https://www.ontarioinvasiveplants.ca/resources/grow-me-instead/ before purchasing or accepting “gifts” of plants.
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