Divide and Conquer: The Secret to a Great-Looking Perennial Garden

As a founding employee of Gardener's Supply, I wore many hats over the years. Now I run Johnnie Brook Creative. My Richmond, VT gardens include a large vegetable garden, seasonal greenhouse, cutting garden, perennial gardens, rock garden, shade garden, berry plantings, container plants, and a meadow garden. There's no place I'd rather be than in the garden.

A regular schedule of dividing ensures a perennial border looks its best.

As spring returns, perennial gardens stir. Cool weather, moist soil. Emerging plants are slow and sleepy. These early spring weeks are the best time for dividing perennials.

If your established perennial garden is 2-3+ years old, chances are good some plants need attention—probably quite a few. The window is small, so no time to waste!

Once perennials exceed ~3 inches and leaf out, dividing becomes traumatic. You may sacrifice current year's blooms—and possibly the entire plant if not careful. A few tolerate early summer division (bearded iris, daylilies); a few only fall division (see below). But for 90%, now is the time.

Why divide? Three main reasons: too large for space; oldest part died out; growth so dense plant no longer blooms well.

Step 1: Dig up perennial to divide. Example: sedum, needing division every 2-3 years.

Step 2: Many clumps are so dense a shovel is needed to cut through root mass.

A healthy chunk, ready for replanting.

Here's how:

1. Unless plant is small, use garden fork/spade to lift entire root ball onto a tarp. (Recruit a strong helper.)
2. Pry root ball into 2+ pieces. If too dense, cut with sharp spade, hand saw, or old serrated kitchen knife. Discard dead/weakened sections.
3. Before replanting, freshen soil with compost and handful(s) of granular organic fertilizer.
4. Replant only healthiest chunks; relocate extras or share with friends.
5. Water deeply and keep roots consistently moist for 2+ weeks while re-establishing.

Division Schedules

Divide every 2-3 years: Aster, Coreopsis, Sedum 'Autumn Joy', Garden mums (Dendranthema), Helenium, Heuchera, Shasta daisies (Leucanthemum), Garden phlox (Phlox paniculata), Yarrow (Achillea)

Divide every 3-5 years: Bergenia, Cranesbill (Geranium), Campanula, Daylilies, Eupatorium, Nepeta, Rudbeckia, Stachys, Veronica

Divide infrequently: Goatsbeard (Aruncus), Hosta, Lady's mantle (Alchemilla), Lungwort (Pulmonaria)

Do NOT divide in early spring: Bearded iris (early summer after blooming), Creeping phlox (fall), Foxtail lilies (fall), Oriental poppies (fall), Peonies (fall)

Do NOT divide at all: Baby's breath, Baptisia, Candytuft, Clematis, Delphinium, Euphorbia, Flax, Foxgloves, Lupines, Monkshood, Rosemary, Russian sage, Trillium, Yucca

More Information

• Fine Gardening magazine has an excellent article on dividing perennials, grouped by root system type with short videos.
• The Well-Tended Perennial Garden by Tracy DiSabato-Aust is a must-have for perennial gardeners—covers planting, staking, dividing, winter care.