Dividing Perennials

By Alex Tisthammer | Fort Collins Nursery

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 pull the rhizomes apart with your hands quickly. You’ll want a decent-sized chunk for each division, 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 not to contaminate all your new plants. When replanting, make sure not to plant the iris too deep! The top of the rhizome should be visible and level with the soil. 

Daylilies: Divide daylilies between the early spring and late fall when they start 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 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 ample time to establish themselves before it gets cold. Once again, dig up the whole plant, getting as much of the root system as possible. 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, many other perennials may be in your garden and will benefit from being divided at some point. Plant division is not only great for your plants but also excellent 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