When dividing perennials, timing and technique are important. Perennial plants are healthiest and most productive when they are young and have room to spread. How wonderful that we can rejuvenate even the oldest residents of a garden by occasionally dividing them. Read on to learn how to divide plants.

1. Divide when a plant looks good

2. Start at the drip line

To lift a perennial with minimal root damage, begin digging at its drip line. The roots will generally extend that far, so digging there lets you lift the plant with most of its roots intact. Dig a trench around the clump, cleanly severing any roots, then cut at an angle down and under the clump from various points around the outer edge until you can lever the plant out of the hole. For large, heavy plants, you may have to first dig the trench, then slice straight down through the center of the plant as if it were a pie, halving or quartering the clump before under­cutting and lifting it.

In early spring, I divide while the new growth is still low to the ground, so the handling of stems is not usually an issue. In summer, I might tie stems together before lifting the plant to avoid damaging them during the digging. In fall, I usually cut plants back before digging them for division.

3. Divide in cool weather

Perennials can be divided at any time of the year if you give them appro­priate care afterward, and I do just that. But for the best return on my time and the quickest reestablishment of the perennials, I divide when the soil is warmer than the air for at least part of every 24-hour period. That’s just before peak daffodil season in spring and in early fall right after the nights become cool. These con­ditions will allow the roots of the division to grow while the tops stay low, out of the sun and wind.

I prefer to divide in the fall rather than in the spring because the plants have more time to set new roots before growing up into the heat. I will divide fall bloomers in Sep­tember if it’s expedient, but I usually leave them to bloom undisturbed and divide them in the spring.

4. Keep roots cool and moist

Fifty percent humidity and 50°F are the ideal conditions for holding divisions until you can get them back into the ground. Put them into a bucket or box in a cool shaded place, such as a garage, and cover them with newspaper to retard moisture loss. Sprinkle water to dampen the newspaper if the roots seem to be drying during their “hold” time. If, despite your best efforts, the divisions dry out while on hold, don’t despair. Soak them in a bucket of water for about an hour before replanting.

5. Replenish soil with organic matter

6. Use vigorous sections first

7. Take extra care when a plant’s in bloom

Although I have often read that I shouldn’t, I sometimes divide plants when they’re blooming. I understand, how­ever, that plants in bloom may not be capable of growing as many new roots as quickly as nonblooming plants. I’ve done this in September when Japanese anemones (Anemone × hybrida cvs.) and asters (Aster spp. and cvs.) are in bloom and in April when the pasque flower (Pulsatilla vulgaris ) and lungworts (Pul­monaria spp. and cvs.) are at their peak.

I haven’t lost any divisions yet. I have also divided late-spring and summer bloomers while they were flowering. Given the extra care that common sense dictates (such as more attentive watering or shade at midday), these plants will fare well too.

10. Let the roots be your guide

When you dig up a perennial, you will see that it fits into one of five basic root types: roots that form clumps or offsets, surface roots, underground running roots, taproots, or woody roots. How you proceed depends on what root type your plant has.

VIDEO  Introduction to Dividing Perennials

Offsets

To divide a plant whose roots form offsets (small plants growing at the base of a larger one), snap the connection between any of the sections to obtain a piece with ample roots and three or more growing points (or “eyes”). Some denser clumps may have to be cut apart.

Plants that form offsets include asters (Aster spp. and cvs., USDA Hardiness Zones 4–8), coneflowers (Echinacea purpurea and cvs., Zones 3–9), hostas (Hosta spp. and cvs., Zones 3–8), and tickseeds (Coreopsis spp. and cvs., Zones 4–9).

VIDEO  Dividing Plants With Roots That Form Offsets

Surface roots

Some perennials have roots that run on or just below the surface of the soil. They form new crowns and roots when they reach open spaces or make contact with the soil. If you cut between any of the stems as you would cut a piece of sod from a lawn, you will have a division with its own stems and roots.

Plants with surface roots include bee balms (Monarda spp. and cvs., Zones 4–9), black-eyed Susans (Rudbeckia spp. and cvs., Zones 3–9), creeping sedums (Sedum spp. and cvs., Zones 3–9), and creeping speedwells (Veronica spp. and cvs., Zones 3–8).

VIDEO  Dividing Plants With Surface Roots

Taproots

Plants that have taproots can be divided by using a sharp knife to slice down the length of the root. Every piece that has at least one eye, some of the taproot, and a few side roots is a viable division.

Plants that have taproots include balloon flowers (Platycodon grandiflorus and cvs., Zones 4–9), butterfly weeds (Asclepias tuberosa and cvs., Zones 4–9), cushion spurges (Euphorbia polychroma and cvs., Zones 4–9), and Oriental poppies (Papaver orientale and cvs., Zones 4–9).

VIDEO  Dividing Plants With Taproots

Underground running roots

Underground running roots can develop suckers as they grow beyond the shade of the mother clump. These suckers can be cut away from the main plant, or you can dig up the main plant and cut away any piece with an eye or sucker already forming.

Plants with underground running roots include hardy geraniums (Geranium spp. and cvs., Zones 4–9), Japanese anemones (Anemone × hybrida cvs., Zones 4–8), ostrich fern (Matteuccia pennsylvanica, Zones 3–8), and plume poppies (Macleaya spp. and cvs., Zones 4–9).

VIDEO  Dividing Plants With Underground Running Roots

Woody roots

Woody perennials often form roots when stems rest on the ground or are buried by gradually accumulating mulch. Make a new plant by simply cutting between the rooted stem and the mother plant.

Plants that have woody roots include candytufts (Iberis spp. and cvs., Zones 5–9), euonymus (Euonymus spp. and cvs., Zones 4–9), lavenders (Lavandula spp. and cvs., Zones 5–10), and sages (Salvia spp. and cvs., Zones 5–10).

VIDEO  Dividing Plants With Woody Roots