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Dividing Perennials

1 Jan 2022 12:00 AM | Brenda Peshak

There are many advantages to growing perennials in your landscape. Perennials require less maintenance since they don’t have to be planted each year. Their root systems are deeper than annual plants which means they require less water and can reach deeper into the soil to gather more nutrients and help improve soil structure.

One of the other great advantages of perennials is the ability to divide them. Dividing perennials may help plants perform better by reducing overcrowding and allowing more room for roots to grow and absorb water and nutrients meaning more vigorous growth and blooming. Dividing can also help manage the size and spreading of plants. If you’ve ever grown mint in your garden, you know of this firsthand. For the frugal gardener, dividing perennials increases the number of plants in your landscape at no cost.

In general, plants should be divided in the opposite season that they bloom. Plants that bloom in late summer and fall (examples: aster, sedum, ornamental grasses) should be divided in the spring after the danger of frost and when new growth is emerging. Plants have stored up energy from the winter that will aid in their recovery; their emerging small leaves will suffer less damage and have the entire season to recover.

Plants that bloom in the spring and early summer (examples: hosta, daylily, peony, daisy) are easy to locate as they are fully established. Plants should be divided at least 4-6 weeks before the ground freezes to allow time for the roots to become established in their new location.

The actual division of perennials can vary based upon the root structure of the plant. The hardiness, size and type of root system should guide you when determining how to divide them.  Below are some general tips when dividing perennials:  

  • If possible, divide plants on overcast days and not during the heat of the day.
  • If possible, water 1-2 days before dividing. This may help ease the digging up of the roots and ensures the plant is less stressed.
  • Pull plants out of soil using a shovel or spade.
  • Remove soil from the roots to more easily determine the best place to divide.
  • Gently pull or tease roots apart with your hands if possible or with knife or spade. Allow the plant to dictate what is needed to divide. For example, Lily of the Valley has smaller delicate roots that can easily be teased apart by hand; however, a large clump of ornamental grasses will require a sharp spade and possibly some muscle to divide.
  • Each division should have 3-5 shoots and healthy roots.
  • Keep divisions moist and shaded until planted in their new location.
  • Plan on watering after transplanting to help the divisions establish.

While the general rules and tips above apply to the majority of perennials, there are always exceptions to the rules. Below are some common perennials that respond well to division and can be divided at different times.

    • Hostas are very resilient perennials that can be divided in either the spring or fall. It’s possible to divide them even in summer if they are kept hydrated and well watered.
Bearded Iris
    • Divide these perennials every 1-3 years.
    • Fewer blooms may mean a need for rejuvenation by division.
    • Divide 4-6 weeks after flowers are finished blooming.
Siberian Iris
    • This particular variety of iris can be divided in spring, late summer or early fall.
    • In the spring divide before leaves are 3-4” tall.
    • In the fall cut leaves to 6-12” then divide.

Perennials are a great addition to any landscape. Consider getting the most out of your plants and help them thrive by dividing them. Plant your divisions in other areas, create a new garden bed or share with friends, neighbors or family.

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