Dividing Perennials

In his column Friel World appearing in Green Profit magazine, John Friel wrote, “A perennial border is evolution on fast-forward, a watercolor in the rain, changing weekly as various species segue in and out of bloom – and yearly as its constituents dominate or yield, flourish or succumb, according to their natures.”

Friel perfectly describes a native perennial border. Each plant grows according to its nature. Some are spreaders while others stay put or fade with competition. To keep all these plants happy and harmoniously growing together, a few plants may need to be thinned from time to time, or divided so that they don’t dominate other species.

When to Divide Your Perennials

As we move into spring, March and April are the best months to begin dividing perennials. You can divide in August and September, but excess growth and heat may hinder success. Any type of disturbance to the root system can be stressful for perennials. Dividing during times with cool, moist conditions will reduce shock. Another thing to keep in mind is that native grasses will not start to actively grow until soil temperatures reach at least 60 degrees. Grasses are often the last plants I divide in the spring. It’s a good idea to wait until they are starting to show signs of life.

Which Plants to Divide • Yarrow • Asters • Coral bells • Joe Pye weed • Gayfeathers • Monarda • Rudbeckia • Coreopsis • Spiderwort • Sneezeweed • Goldenrod • Purple Coneflower varieties • Ironweed • Sunflowers

After several seasons of growth, native grasses often form a “donut”. The center dies back while the active growth continues around the outer edges. • Switchgrass • Little Bluestem • Big Bluestem • Indiangrass • Sideoats • Blue Grama

The prairie perennial bed at our front entrance sign will benefit from division of plants, especially the grasses and asters. This switchgrass would benefit from being divided too.

How to Divide Perennials Dig the Clump

After you have identified the plants that need to be divided, the next step is to dig the entire clump out of the ground. If the soil is dry, it is beneficial to water the area a few days ahead of time to soften the soil. Well-established grasses can be challenging to dig, but it is important to work at it until it is completely removed. Grasses are resilient and can take much abuse in this division process. I have even worked at removal with a pick axe. Remove the clump or clumps from the hole and set it aside. Brush off excess soil to reveal the growing points.

Separate the growing points/ crowns and replant

Some plants are easier to pull apart than others. For instance, asters are easier to pull apart than switchgrass. Usually, I break these clumps into 4, 8 or 16 pieces with a pruner, lopper, shovel or axe. Each clump needs to have a few leaves or healthy growing points and roots in order to grow. Then, replant the divisions as soon as possible so the roots don’t dry out. I put them back into the same hole from which they were removed. Plant at the same depth as before and water well. Cover any bare soil with mulch to help conserve moisture while your new divisions become established. The leftover plants can be shared with friends or composted.

Water well

Reestablish these divisions as you would any newly planted perennial. Water daily, or every other day depending on the weather, for the first two weeks. Once you see new growth, reduce water frequency to every other day or every three days. You have removed much of the supporting root system, so it will take at least a season to get that back. Also, I would not fertilize the new transplants, because this will encourage top growth that is not sustainable with the new root system.

Which Plants to NOT Divide

While most perennials benefit from being divided every few years, there are a few perennials with deep taproots that are better left alone. You will be more successful planting new seedlings than trying to dig these plants out of the ground. In my experience, it is easier to start with a plant than to remove these plants. Too much damage is inflicted on the taproot. Avoid dividing these varieties: • Wild Indigo (Baptisia sp.) • Compass Plant • Butterfly weed (Asclepias) • Coneflowers (Echinacea angustifolia, Echinacea pallida, and Echinacea paradoxa)

At the Dyck Arboretum of the Plains, we have divided and transplanted hundreds of plants over the years and I don’t believe we have ever lost one. Native perennials are resilient and begin to recover from being transplanted in about a week. They may look stunted or peaked the first year, but they will really come to life the next year. As you begin your garden planning in the next few weeks, go out and identify a few plants that would benefit from a fresh start.

SCOTT VOGT Horticulturist

Scott Vogt is Executive Director at Dyck Arboretum of the Plains in Hesston, KS, where he has worked with native plant displays, consultations, designs and education since 1997. He is an author of numerous articles and a frequent contributor to the Arboretum’s weekly blog, ‘Prairie Notes’. He has worked to expand FloraKansas Native Plant Days, the largest native plant sale in the state (April, September). Learn more at www.dyckarboretum.org, Facebook, and Instagram.