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Dividing Perennials

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DIVIDE AND CONQUER

A perennial border packed with interesting leaf textures and colorful, fragrant blossoms is truly a treat for the senses. Unfortunately, if your perennial plants are overcrowded, they must struggle to compete for nutrients and water while restricted air circulation creates conditions that foliar diseases and fungus thrives on. Perennial plants vary widely in their growth habits and growth rate. Some grow slowly taking a long time to become established, while others grow so quickly that they threaten to take over the garden! Division is a useful (and free!) technique to help keep your perennials neat, healthy, and in peak bloom.

When to Divide

  • The vast majority of perennials respond best to being divided in early spring, just as new growth is emerging. Root systems are full of stored energy to help the divisions recover from being cut apart.
  • Divide when weather is cool and there is plenty of moisture in the soil.
  • Spring divisions also have an entire growing season to recover from the stress of division and develop the strong roots needed to survive Colorado’s harsh winters.

Methods of Division

  • There are two basic methods of dividing perennials. One is to cut them apart, the other is to pull or tease the roots apart.
  • Determine which method is best suited to your plant by examining its root system and growth pattern.
  • Start by digging up the entire clump. Tough, dense roots (like those of Peony) will need to be cut apart with a sharp knife or spade.
  • Tangled, fibrous roots (such as Coreopsis) can be separated by hand, or by inserting two garden forks placed back-to-back and then pulling them apart.

Division Guidelines

  • Divide your perennial if the center has died out. The roots in the center of the clump can become densely overcrowded and do not receive the nutrients or water that the plant needs to thrive.
  • Divide plants that have fewer or smaller flowers than in previous seasons.
  • See below for a list of recommendations for how frequently to divide certain plants. Perennials that are watered, weeded, and fertilized on a regular basis may need to be divided more frequently due to their potential for more vigorous growth.

Suggestions on what plants to divide when:

DIVIDE IN EARLY SPRING
EVERY 1-3 YEARS

  • Aster
  • Beardtounge (Penstemon)
  • Beebalm (Monarda)
  • Coralbells (Heuchera)
  • Cornflower (Centaurea)
  • Delphinium
  • Dianthus
  • Foamflower (Tiarella)
  • Garden Mums (Dendranthema)
  • Obedient Plant (Physostegia)
  • Painted Daisy (Tanacetum)
  • Shasta Daisy (Leucanthemum)
  • Spiderwort (Tradescantia)
  • Tall Phlox (Phlox paniculata)
  • Tickseed (Coreopsis)
  • Yarrow (Achillea)

DIVIDE IN EARLY SPRING
EVERY 3-5 YEARS

  • Astilbe
  • Bellflower (Campanula)
  • Black-Eyed Susan (Rudbeckia)
  • Blanket Flower (Gaillardia)
  • Catmint (Nepeta)
  • Daylily (Hemerocallis)
  • Gayfeather (Liatris)
  • Jacob’s Ladder (Polemonium)
  • Mallow (Malva)
  • Polygonatum (Soloman’s Seal)
  • Sea Thrift (Armeria)
  • Speedwell (Veronica)

DIVIDE IN EARLY SPRING
INFREQUENTLY, EVERY 5-10 YEARS

  • Cranesbill (Perennial Geranium)
  • Goatsbeard (Aruncus)
  • Hosta
  • Japanese Anemone
  • Lady’s Mantle (Alchemilla)
  • Lungwort (Pulmonaria)
  • Oxeye (Heliopsis)

DIVIDE IN LATE SUMMER OR EARLY FALL
EVERY 3-5 YEARS

  • Asiatic Lily
  • Iris (Bearded, Siberian, Dwarf)
  • Peony (*Divide every 5-10 years)

DO NOT DIVIDE

  • Baby’s Breath (Gypsophila)
  • Balloon Flower (Platycodon)
  • Bugbane (Cimicifuga)
  • Butterfly Weed (Asclepias)
  • False Indigo (Baptisia)
  • Flax (Linum)
  • Gentian (Gentiana)
  • Lupine (Lupinus)

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