Dividing Perennials in Fall

October 16, 2014 12:00 am

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Dividing Perennials

Many gardeners are in the know on this method of multiplying your favorite perennials… but it can still seem like a daunting task if you have never tried it before. Let us put your mind at ease a bit. Splitting perennials in the Fall can be some of your best time spent in the garden. Not only can it enhance the vigor of your current landscape plantings, but it can also multiply select choices… enhancing the density and diversity of your garden.

We found a fantastically educational article from the Clemson University (www.clemson.edu) that helps illustrate what we’d like to share with you. We promise, just give it a try, you will not be sorry you did!

Root Systems

Perennials generally come in three different root system types:

  • Spreading
  • Clumping
  • Tuberous

Spreading root systems have a fairly irregular habit, matted and slender in nature… lacking a distinct pattern. They are generally the easiest to divide, as it can easily be done by hand, but pro’s prefer to cut them apart with shears or a knife.

These perennials can get out of hand pretty quick, so it’s a good idea to divide them frequently as to not become intertwined with other nearby plants. Commonly well-known members of this variety are Asters, Bee Balm, Lamb’s Ear and Echinacea.

Spreading Root System Illustration

Clumping root systems are a bit more involved in the division process as their root mass is thick and not as simple to pull apart. Because of the thicker, fleshier nature of clumping root systems, it’s necessary to cut through the crown of growth directly above the root mass. This makes it easier to pry the ball into multiple clumps. Common perennials to this group are Astible, Hosta, Daylily and most ornamental grasses.

A sub-set of clumping root systems are those of the Rhizome nature. Rhizomes are stems that grow horizontally along the surface of the soil. Because the roots of such plants (Iris being the most commonly known) are more exposed to the elements, they’re also more susceptible disease and pests.

Clumping Root System Illustration

Rhizome Root System Illustration

The last major grouping of perennials are the Tuberous. Tubers are generally grown from bulbs, Dahlias being one of the popular choices. Tubers should be cut apart with only a sharp knife, as to be precise enough to get a cutting that includes some of the original stem AND a growth bud attached. You can either directly plant the freshly split tuber, or store it for Spring planting.

Tuberous Root System Illustration

DON’T divide these perennials!

Of the many perennials that benefit from scheduled division… there are a select few that should NOT be divided. Some simply do not like the habit, while others develop a woody stock and shouldn’t be divided, otherwise to their detriment.

These selections include, but are not limited to:

  • Euphorbia
  • Oriental Poppies
  • Japanese Anemones
  • Columbine
  • Lavender
  • Candytuft
  • Artemesia

Planting the Divisions

Three simple tips can make all the difference when planting your freshly divided perennials:

  • NEVER allow the divisions to dry out.
  • Trim damaged or broken roots before replanting
  • Cover the freshly planted divisions with a generous layer of mulch, 2″ is what we recommend. This will ‘blanket’ the tender little guys over the winter months and super-charge growth in the Spring.

Further details or a more comprehensive set of instructions, please visit the actual article site, by clicking here.
For quick reference, below is a table of common perennials, how to divide them, when to divide them and the method of division:

When and How to Divide Some Common Perennials

Common Name
Botanical Name
How Often To Divide
Season To Divide
Method Of Division

Asters
(Aster)

Every year or two to control spread and maintain vigor.
Spring

Spreading root division. Replant outer growth and discard the centers of older plants.

Astilbe
(Astilbe)

Every 2 to 3 years as plants become crowded. Early Spring or fall.

Spreading root division. Needs division for best bloom.

Bearded Iris
(Iris)

Every year or two to control spread and maintain vigor.
Spring

Rhizome root division.

Beebalm
(Monarda)

Every 3 years to control rampant growth. Spring or fall.

Spreading root division.

Bellflower
(Campanula)

Every 2 to 3 years or as the plant becomes crowded. Spring or early fall.

Spreading root division.

Blackberry Lily(Belamcanda)

Every 3 to 4 years after bloom is finished.

Rhizomes should be treated as iris.

Black-eyed Susan
(Rudbekia fulgida)

Every 3 to 4 years. Early spring or fall.

Spreading root division.

Blanket Flower
(Gaillardia grandiflora)

Every 1 or 2 years to maintain vigor. Early spring.

Spreading root division.

Bleeding Heart
(Dicentra)

Rarely needs division. Early spring.

Fleshy root division. Be gentle with brittle roots.

Cannas
(Canna)

Every 3 or 4 years, or as desired to increase stock. Spring.

Fleshy root system.

Chrysanthemum
(Chrysanthemum)

Every year or two. Spring.

Spreading root division.

Cranesbill
(Geranium)

Every 2 to 4 years. Spring or fall.

Spreading root division.

Daylily
(Hemerocallis)

Every 3 to 6 years or as desired to increase stock. Spring, summer or fall. Ideal time is after bloom is finished.

Divide fleshy roots into segments with roots. Divisions with three or more shoots will bloom sooner.

Garden Peony
(Paeonia)

For plant increase, rarely needs division. Divisions may wait up to 3 years before blooming. September or October.

Divisions should have three to five well-developed eyes (buds for next year’s growth). Plant peonies with the eyes no deeper than 1 inch below the surface.

Garden Phlox
(Phlox paniculata)

Every 3 to 4 years. Early spring or fall.

Spreading root division.

Hosta
(Hosta)

Rarely need division and will reach their best form if not divided too often. They can be divided as needed for plant increase. Early spring or early fall.

Fleshy root division. Divide into clumps with one to three eyes. A wedge can be taken from an established plant, which will soon fill back in.

Lambs-ear
(Stachys byzantina)

Every 2 to 3 years. Spring or early fall.

Spreading divisions. Discard weak centers.

Lily of the Nile
(Agapanthus)

When flowering slows due to crowding.
Spring, summer or fall

Fleshy clumping roots are large and brittle. Do not divide unless needed to improve bloom.

Lily of the Valley
(Convallaria majalis)

Divide for plant increase as desired. Early spring.

Can be divided as clumps or single “pips”.

Ornamental Grasses

Every 3 to 4 years. Spring for most grasses. Many grasses do not tolerate fall division.

Very dense fibrous root system may require the use of an ax or saw to divide.

Purple cone-flower
(Echinacea)

Every 4 years. Spring or fall.

Spreading root division.

Red-hot-poker
(Kniphofia)

Divide only for plant increase. Spring or fall.

Fleshy clumping root system. Divisions may take 2-3 years to bloom.

Tall sedum
(Sedum ‘Autumn Joy’)

For plant increase. Spring.

Clump divisions.

Tickseed
(Coreopsis)

Every 1 or 2 years to maintain vigor. Spring or fall.

Spreading root division. Discard weak center.

Wormwoods
(Artemisia)

Every year or two for spreading wormwoods like ‘Silver King’ and ‘Valerie Finnis.’ Spring.

Spreading root division, or remove excess and dead center. Do not divide woody artemesias.

Yarrow
(Achillea)

Every 2 or 3 years or when center dies out. Spring or fall.

Spreading root division.