Why divide? Size control Rejuvenation Increase number When to divide? Dividing Perennials Perennials growing in optimum conditions can generally be divided every 3-5 years Signs that plants should be divided Increasingly smaller flowers each year or does not bloom at all Centers of clumps die out Divide on a cloudy day to reduce water stress Spring and summer blooming divide in fall o September thru October o Allow 4-6 weeks before ground freezes Fall bloomers divide in spring o When new growth tips emerge, but before hot weather sets in o May delay flowering Preparations Prune stems and foliage to 6 for easier dividing and to reduce water loss Try to leave some new foliage on plant Water plant ahead of time Prepare area to plant new divisions Tools needed Knife, Machete, Shovel, Hands, Saw, or Axe
Dividing Different Root Systems Clumping- Hosta, Astilbe, Daylily, Ornamental Grass Spreading- Aster, Echinacea, Monarda Lift Dig 4-6 deep around plant Pry plant up from underneath with spade or fork Shake or hose off loose soil to find best division points Separate Locate natural division points and buds to decide how to split up clump Leave 2-3 new shoots and buds/plantlet Trim broken, long roots, pull out old woody stems Keep moist Do not let divisions dry out, will affect re-establishment o Especially ornamental grasses! Plant Replant to base of crown or to level where stem/foliage/roots meet Firm soil around plant, water well Mulch Rhizomes Divide Iris one month after flower until fall. Leave a few inches of rhizome and one fan of foliage- cut back to just above where fan begins to divide. Replant with the top of rhizome showing just above soil level. Tuberous Roots Cut tuber apart with sharp knife, leaving a portion of original stem and growth bud attached. Replant or store until spring.
WHEN AND HOW TO DIVIDE SOME COMMON PERENNIALS Botanical Name Asters (Aster) Astilbe (Astilbe) Bearded Iris (Iris) Beebalm (Monarda) Bellflower (Campanula) Blackberry Lily (Belamcanda) Black-eyed Susan (Rudbeckia fulgida) Blanket Flower (Gaillardia grandiflora) Bleeding Heart (Dicentra) Cannas (Canna) Chrysanthemum (Chrysanthemum) Every year or two to control spread and maintain vigor. Spring Every 2 to 3 years as plants become crowded. Early Spring Every 3 to 4 years. After flowering up to September. Every 3 years to control rampant growth. Spring Every 2 to 3 years or as the plant becomes crowded. Spring or early fall. Every 3 to 4 years after bloom is finished. Every 3 to 4 years. Early spring Every 1 or 2 years to maintain vigor. Early spring. Rarely needs division. Early spring. Every 3 or 4 years, or as desired to increase stock. Spring. Every year or two. Spring. Replant outer growth and discard the centers of older plants. Needs division for best bloom. Rhizome root division. Rhizomes should be treated as iris. Fleshy root division. Be gentle with brittle roots. Fleshy root system.
Botanical Name Cranesbill (Geranium) Garden Peony (Paeonia) Garden Phlox (Phlox paniculata) Hosta (Hosta) Lambs-ear (Stachys byzantina) Lily of the Nile (Agapanthus) Lily of the Valley (Convallaria majalis) Ornamental Grasses Purple cone-flower (Echinacea) Red-hot-poker (Kniphofia) Every 2 to 4 years. Spring or fall. For plant increase, rarely needs division. Divisions may wait up to 3 years before blooming. September or October. Every 3 to 4 years. Early spring 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. Every 2 to 3 years. Spring or early fall. When flowering slows due to crowding. Spring, summer or fall Divide for plant increase as desired. Early spring. Every 3 to 4 years. Spring for most grasses. Many grasses do not tolerate fall division. Every 4 years. Spring Divide only for plant increase. Spring 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. 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. Spreading divisions. Discard weak centers. Fleshy clumping roots are large and brittle. Do not divide unless needed to improve bloom. Can be divided as clumps or single "pips". Very dense fibrous root system may require the use of an ax or saw to divide. Fleshy clumping root system. Divisions may take 2-3 years to bloom.
Botanical Name Tickseed (Coreopsis) Yarrow (Achillea) Every 1 or 2 years to maintain vigor. Spring Every 2 or 3 years or when center dies out. Spring Discard weak center. Perennials that Don t like to be Divided Asclepias Euphorbia Papaver Gypsophila Dictaminus Baptisia Aquilegia Helleborus Santolina Iberis Lavender Rosemary Dianthus Digitalis Perovskia