Dividing Perennials

By Alex Tisthammer

In order to keep your landscape healthy, attractive, and blooming, it is important to divide certain perennials. The plants we get asked about the most are daylilies, iris and ornamental grasses. These are also the ones that usually exhibit stress when it is time to divide them, either through not blooming or dying out in areas. Here are some helpful tips to help you determine when and how to identify these popular landscape plants:

Iris: Iris can be divided in spring or late summer, but with spring division you are likely to lose that year’s blooms, so many prefer to do this when they are dormant in summer. First, cut the foliage back to one third. Then, dig up the whole clump with a shovel or trowel. You should be able to easily pull the rhizomes apart with your hands. For each division, you’ll want a decent sized chunk, about the size of your thumb and with a few leaves on it. Make sure to discard any hollow or unhealthy looking rhizomes. If you notice any unhealthy rhizomes, sanitize your tools between each division so as to not contaminate all your new plants. When replanting, make sure not to plant iris too deep! The top of the rhizome should be visible and level with the soil. 

Daylilies: Divide daylilies in the early spring or in late fall when they are starting to go dormant. Dig up the whole daylily (this can be quite a chore if you’ve waited too long to divide!) Once the whole plant is out of the ground you can shake off all the dirt clinging to the roots to properly see the root system. At this point you will be able to see clear division points where you’ll want to cut. Choose a dividing tool – a sharp pair of scissors or even a bread knife – and start cutting into the plant to create your divisions. Each division should have a good amount of roots and at least three stems. 

Ornamental Grasses:  Divide in spring or midsummer when the grass is actively growing but not flowering. This gives the new plants plenty of time to establish before it gets cold. Once again, dig up the whole plant, getting as much of the root system as you can. Then cut it into sections with a sharp shovel or knife, usually two or more, and remove any dead/brown areas.

Iris, Daylilies, and Ornamental Grasses are the most commonly divided plants, however there are many other perennials that may be in your garden and will benefit from being divided at some point. Division is not only great for your plants but also is great for you and your neighbors – free plants! 

  • Hostas
  • Coneflowers
  • Poppies
  • Bulbs that have naturalized (grape hyacinths, daffodils, tulips, crocus)  
  • Bee Balm
  • Bachelor’s Button
  • Catmint
  • Columbine
  • Dianthus                                                       
  • Fall Anemone
  • Goldenrod
  • Hardy Geranium
  • Joe Pye Weed
  • Lamb’s Ear
  • Shasta Daisy
  • Sedum
  • Yarrow

Originally published on August 25th, 2023.