Dividing perennials in fall

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Lily of the valley

Lily of the valley. Photo by Liz West, Wikimedia Commons.

The continuation of this beautiful summer-like weather into autumn has many people still actively gardening. Luckily, this is an ideal time to divide many varieties of perennials, and the weather is ideal for gardeners to enjoy this task.

Most plants are pretty tough and are just fine when divided. Some perennials prefer not to be divided at all, however, while others actually do better on the move and should be divided to keep them healthy and happy. So which is which?

There is a basic rule that applies to many perennials: If the plant blooms in spring or early summer, divide it in the fall. If the plant blooms mid-summer to fall, divide it in the spring. It takes a great amount of energy for a plant to flower, so by dividing when it is not in bloom, the plant will use its energy to grow healthy roots, which will give it a stronger start and a better chance of surviving and thriving.

To further increase a plant’s best chances:

  1. Prepare new holes or pots (to give away to friends and neighbors) before you dig and divide.
  2. Start to dig at the drip line and lift the whole plant onto a tarp or into a wheel barrow.
  3. Transplant the most vigorous roots first, then the smaller ones.

Perennials to divide and relocate now

Lilies. Photo by F.D. Richards, Wikimedia Commons

Lilies. Photo by F.D. Richards, Wikimedia Commons

  • Astilbe (use a hand saw)
  • Asiatic lily
  • Oriental lily
  • Lily of the valley
  • Veronica
  • Peony (use a hand saw)
  • Siberian and Japanese iris

In addition to dividing established plants, now is an ideal time to plant spring flowering bulbs and garlic. Since you’ll already be digging a hole or two, might as well make it a little wider and add in a little extra flower power and something extra to look forward to next spring!

Perennials that like to be divided and perform better when they are include daylilies, peonies, Black-eyed Susans, iris, and upright sedum (which will start to die out in the middle when it’s ready).

These perennials prefer not to be divided

  • Delphinium
  • Euphorbia
  • Foxgloves
  • Geraniums
  • Salvia
  • Russian sage
  • Artemisia
  • Trillium
  • Also, anything with a taproot resents being divided, including asclepias (butterfly weed), baptisia, and lupine.

It may seem that this list is missing a key player. So what about hostas? These nearly indestructible plants can be divided spring or fall. Spring is the simplest time because the newly emerging leaves and stems are easy to see and work with. But fall is also great thanks to cooler temperatures and (usually) ample rainfall.

The real question is why the plants are being divided. In general, dividing hostas sets them back a couple years; they usually perform better as they get older and bigger. Good reasons to divide or relocate hostas are to make more plants for your garden or to share, or because they are crowding other plants. If dividing, using a spade works best. Otherwise, feel free to leave hostas alone and let them become as big as they’d like to be.

For more information visit the University of Minnesota Extension website: http://www.extension.umn.edu/.


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