Dividing Perennials

What to divide?

Dividing  perennials allows you to multiply your plants and to improve plant health. Perennials that require dividing are clump forming. i.e. perennial grasses, irises, anemone, hosta, daylily, etc. Plants benefit from division every 2-3 years to improve health and vigor. You'll know that a plant needs to be divided if it has less flowers or smaller flowers than usual. Plants may also exhibit die back in their centers if they aren't divided in time. This results from growth in the center of the plant becoming too dense. New growth may only occurring on the outside of the plant when center growth is too dense. It also manifests with a lack of bottom leaves and floppy stems. Get to know your garden and be on the lookout for signs that plants need to be divided.

When to divide?

  • Spring flowering perennials, like irises, should be divided in the Summer or Fall.
  • Summer flowering perennials can be divided in Spring or Fall.
  • Fall flowering perennials are best divided in the Spring.
  • Warm-season grasses will turn brown and go dormant in cooler temperatures. These types of grasses should be divided in the Spring or early Summer when they are actively growing so that your divisions can take hold in the landscape.
  • Cool season grasses continue growing in lower temperatures and should be divided in Spring or Fall when they are still actively growing.
Tip: Always wait until a plant is no longer flowering to divide so that the plant can focus energy on root growth instead of flower retention.

How to divide?

When dividing perennials use a spade or pitchfork to dig the mother plant, ensuring that you dig a large enough root ball to not damage the roots. Remember the success of a divided plant will depend on its root system. Carefully remove any excess dirt from the root ball, but you cannot repair damaged roots.

Make an assessment once the mother plant is out of the ground. The size of divisions is usually up to you. Ensure that each division contains an adequate number of roots and shoots to ensure success when transplanting. Plants with fibrous root systems can be divided by hand. A dense root system or fleshy roots require gardening tools  to divide the plant. Plants with dense root systems can be divided using two pitchforks, inserted at the crown of the plant, to pry the divisions apart. In some instances, a spade or saw may be necessary to divide a plant as is often the case in plants with fleshy root systems like peonies.

Once you have made your divisions either transplant immediately or store in a shaded location. The plants will be more susceptible to drying out above ground because of root exposure and stress from dividing.

Tip: When dividing plants in the Fall always allow for a 6-week window before the ground freezes so that divisions have time to establish.