from the employee owners at Gardener's Supply Co.

Dividing Vigorous Perennials

Beebalm (monarda)

Beebalm (monarda) spreads to form large colonies that need frequent dividing to keep them within bounds and blooming vigorously. Customer photo from Cheryl S. of Copley, Ohio. See the full-size photo in the Dutch Gardens Photo Center.

Community plant sales and swaps are a highlight of the gardening season at this time of year. These events are ideal places for new gardeners to hook up with seasoned veterans and for surplus plants to find new homes.

Perennials that spread readily and those that need frequent dividing make up the core offerings at these events. Vigorous creepers, such as like beebalm (Monarda), yarrow (Achillea), lily-of-the-valley (Convallaria), obedient plant (Physostegia), and common yellow sundrops (Oenothera fruticosa) can easily take over the garden if allowed to grow unchecked. Digging up the colony and replanting part of the population every couple of years keeps each in its allotted space.

Some perennials grow in dense or ever-expanding clumps that eventually stop blooming or simply die in the middle. These include tall phlox (Phlox paniculata), Shasta daisy (Leucanthemum), blanket flower (Gaillardia grandiflora), tickseed (Coreopsis), Siberian iris (Iris siberica) and lamb’s ear (Stachys byzantina). Dividing the clump into smaller pieces rejuvenates the original plant and gives you lots of new plants to share with others or to put in other parts of your own garden.

This clump of monarda is ready to be divided.

Dividing and replanting perennials also gives you a good opportunity to replenish the soil. Whenever I move or replace a plant that I’ve divided, I add a shovelful of compost and a handful of slow-release, granular, organic fertilizer to the backfill.

Early spring is the best time to divide summer-blooming perennials—ideally when they are still dormant or just as they emerge from soil. I try to complete the job before the stems get more than a couple of inches tall. As plants leaf out, it gets trickier to divide them because their soft new growth is susceptible to drying out, wilting, and breaking. That said, there’s always a long list of chores for early spring and it’s often mid-May before I’ve divided and moved all the perennials that need it. As long as you make the moves on an overcast day and keep the plants well watered for a couple weeks, most of them will be fine.

Using forks, it’s easy to get the clump out. Take a healthy piece for replanting and use the remaining divisions elsewhere—or share them with other gardeners.

I usually start by digging out the entire clump with a garden fork or spade and putting the plant on a tarp to contain the soil and debris. Some plants are easy to pull apart by hand (beebalm), but others take some serious muscle (tall phlox) and the prying action of a couple of garden forks placed back to back. A few are so tough (Siberian iris), that it’s tempting to resort to a machete or hand saw to get them apart. Regardless of the plant’s tenacity, I make sure that each division has plenty of roots and several vigorous shoots. A few of the largest divisions go back—into the garden with a thorough watering and the rest get potted up and labeled for the garden club’s plant sale in May.

For lists of perennials that need frequent dividing and more details on how to do it, visit these web sites:

-Ann Whitman, Horticulturist

2 Comments

  1. April 30, 2008    

    This was very helpful, and thank you for including the links. I can’t wait for the next good gardening day to get out there and start dividing things, including my dianthus — I didn’t even know I could or should!

  2. April 30, 2008    

    I make it a habit to divide as many plants as I can. That’s what us poor gardeners do.
    http://www.myworkathomedaddy.com

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