When and How to Divide Perennial Plants

Many perennials can be divided simply by pulling apart the roots of dug-up clumps. Susan Weigel

Many perennials can be divided simply by pulling apart the roots of dug-up clumps. Susan Weigel

Dividing your perennial flower plants is an easy way to expand your garden at no cost, with minimal effort required. The technique not only gives you free plants, but is a great way to contain the spread of perennials growing where you don’t want them, invigorate plants who are dying in the center, or share your favorite plants with friends!

When to divide?

Early spring and early fall are two excellent times to divide most species. That timing gives roots several weeks to establish at a lower-stress time than during the peak heat of summer. In general, divide perennials when they’re not blooming or about to bloom.

  • Fall bloomers are best divided in fall. This includes plants such as mums, asters, sedums, goldenrods, and Japanese anemone.
  • Spring bloomers are best divided in spring and include plants such as creeping phlox, foamflowers, salvia, sweet woodruff, and dianthus.
  • Mid-summer bloomers can be divided either at the beginning of the growing season or late summer to early fall – after they’re done blooming.

How often to divide

When determining how often you should divide your perennials, follow these guidelines:

  • Perennials more vigorous in nature benefit from regular division every year or two. These include yarrow, astilbe, campanula, coreopsis, dianthus, gaillardia, beebalm, phlox, geum, helenium, and veronica.
  • Some perennials can go five or even 10 years or more without division, such as hosta, amsonia, barrenwort, ferns, gaura, hardy geranium, lungwort, peonies, and goats beard.
  • There are a few perennials that shouldn’t be dug and divided at all, especially those with deep, single tap roots. These include baptisia, Russian sage, butterfly weed, baby’s breath, artemisia, lavender, sea holly, and bugbane.

If you aren’t sure which category your perennial falls under, doing a simple online search should be able to give you info on how often it can be divided.

Dividing the plant

Dividing perennials is a simple, three-step job:

  1. Dig up the plant or a section of it, digging at the 'drip line'
  2. Pull or cut the plant into two or more fist-sized pieces
  3. Replant the divisions as you would a new plant (ensuring you replant at the same depth as the original plant
  4. Keep it watered

Some perennial plants simply pull apart once you’ve dug them. Just grab a section of stems with each hand and pull until the roots come apart. These easy dividers can include black-eyed susans, coneflowers, hardy geraniums, lamium, Shasta daisies, salvia, foamflowers, and, most of the time, daylilies, liriope, and asters.

Other plants have roots that are tightly interwoven, so you’ll have to use a shovel, knife, or even an ax to split these clumps. These include ornamental grasses, astilbe, hosta, sedum, yarrow, mums, coreopsis, dianthus, ferns, and catmint.

After you’ve replanted the divisions, you should treat them as if they were new plants when considering how much you should tend to them with water and fertilizer. If possible, divide your perennials just before it is supposed to rain. The cooler weather and moisture will help the plants recover from the stress of dividing and replanting.

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