How to Divide and Transplant Perennials

Dividing and Transplanting Garden Plants

8/21/2020

 

• What’s the best way to get more of the plants you love? Divide the ones you have. On the other hand, this isn’t the only reason to divide: Sometimes plants need to be split — they’ll let you know when it’s time.
• The good news is that the process is simple and easy to do.
• Though it looks a little different depending on the roots of the plant.

Basics to make sure you divide your plants in the right way and at the right time:

• Signs that your plants need to be divided (indicators that the plant is getting overcrowded):
• Smaller leaves
• Clumps that are dying out in the center
• Fewer, smaller flowers

Timing & Technique

• When dividing perennials, timing and technique are important.
• Perennial plants are healthiest and most productive when they are young and have room to spread.
• You can rejuvenate even the oldest residents of a garden by occasionally dividing them
• Don’t wait until a plant has become decrepit or monstrous to divide it.
• The rule of thumb is when it looks its best, divide it at the end of that year.
• Watch for the early signs of trouble: when the center of the plant has smaller leaves, fewer flowers, and weaker blooming stalks than the outer edges
• Like this Sedum ‘Autumn Joy’
• Or when the plant runs out of growing room on its edges and has nowhere to go but into neighboring plants.

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 was a pie, halving or quartering the clump before under­cutting and lifting it.

Seasonal handling differences

• 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.

 

Divide in cool weather

• Perennials can be divided at any time of the year if you give the plant appro­priate care afterward.
• 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 in 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.

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.

Replenish soil with organic matter

• If you remove a wheelbarrow full of perennials, then you should put a wheel­barrow full of compost back into that site before replanting to renew the soil, stay ahead of pest problems, and maintain fertility.
• Without additions, the plants will not have the advantage of renewed, fertile soil and the bed will settle after planting, putting the plants at a disadvantage in terms of drainage and air circulation.

Use vigorous sections first

• After dividing, replant pieces that are, at most, 20 to 25 percent of the original clump.
•  Smaller sections grow more vigorously and tend to produce stronger, longer-lasting blooms.
• Dividing a hosta, for example, into pieces with about seven growing points will yield the best results.
• Perennials multiply exponentially—one stem is likely to triple or quadruple itself each year.
• So if all you do is halve an overgrown clump this year, it will more than double in a season and need dividing again the next year.

Keep only the healthiest pieces

• The division on the right came from the crowded center of an old clump of Astrantia carniolica and consequently has fewer roots than the piece from the outside (left).
• The division from the center will grow, but not as fast as the outer one.
• Look for signs of poor health.
• The cut peony stem shows a symptom of disease, and replanting as is will ensure that all new shoots and buds will be exposed to that infection.
• If you wait until a perennial is declining, has a dead center, or has succumbed to pest problems because it has become crowded and weak, be sure to replant only the healthiest pieces.
• Usually these are the outside sections.
• Watch for discolored stems and eroded crowns and roots.

Spread out your divisions

• Replant divisions in a wide hole and over a wide area.
• Spread out the roots wide and down over a mound of soil.
• In the next growing season, the top of the plant will be as wide as the roots are at the time of plant­ing.
• Ensure that when you spread out the roots they don’t overlap and compete with the other divisions.
• Place a division into a hole that is at least as wide as its roots when spread out.
• Don’t turn a root tip up rather than down or curl it back around on itself to fit it into an undersize hole, because you’ll defeat the plant’s natural regrowth mechanisms.
• Root tip growth is regulated in part by chemicals flowing down from the tips of leafy stems to the roots. As in all flows, gravity is involved, so if you plant a root tip up when it was down, the normal flow is interrupted.
• At least temporarily, that root tip will not grow as vigorously as it could.

 

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
• woody roots

• How you proceed depends on what root type your plant has.

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),
• tickseeds (Coreopsis spp. and cvs., Zones 4–9).

 

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, 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).

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),
• Oriental poppies (Papaver orientale and cvs., Zones 4–9).

 

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).

 

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)
• sages (Salvia spp. and cvs., Zones 5–10)

Dig out plants to divide them

• A good rule of thumb is to dig 4 to 6 inches away from the base of the plant.
• That way you’ll get plenty of roots as you lift the clump out of the ground. In the photo, the phlox has been dug all the way around.
•  Actually, there is no need to completely lift the plant up and out — all of that soil can be heavy.
• Instead, the easy method is to simply tilt the whole mass of soil back on the blade of the spade to see the roots and break, or cut, the old plant into smaller sections.
• Often the soil falls away.
• If not, scrape or shake some of the excess off so you have some “wiggle” room to gently pull or cut the divisions.

Dividing tip

• Sometimes the roots are easy to break apart with your hands or a shovel, but for tough and strong roots, a soil knife with a serrated edge makes the task easier.

Look at the roots

• After you dig out the plant, take a look at the roots before starting to separate the plant.
• Not all perennials have the same types of roots.
• Make the correct cut based on the different types of roots.
• Look at the illustrations in the following slides to see which category the plant fits into.

3 ways to divide perennials

• Most perennials fall into one of three categories — 
• Spreaders
• Clumpers
• Plants with Woody Crowns 
• Each type has a few quirks you need to know as you dig the plant out of the ground and separate it into new plants
• See each next:

Spreaders
Find the new crowns around the parent plant and slice down between them.

Clumpers
Cut a large clump like this into three or four sections and replant.

Woody crowns
When dividing, leave at least one set of leaves attached to the main root and replant.

When’s the best time to divide plants?

• If possible, choose a cool and cloudy day to dig perennials out of the ground.
• Spring or fall is usually less stressful than the heat of summer.

Tips for transplanting in hot weather

• Dividing and transplanting in cool weather isn’t always practical. In July, if you find you need to move a plant, even though it’s 90 degrees and sunny, here are some secrets that will help ensure your plants’ survival
• Start by watering the plant and its future home the day before you dig.
• The next day cut the foliage back by half: This way a smaller root system won’t have to support lots of foliage in the heat.
• Next, dig the hole where the new divisions will be set.
• You’re now ready to dig the plant out of the ground and divide just as you would at any other time of year.
• Once you have a division set into its new spot, fill the hole halfway with soil and soak it thoroughly.
• Fill the hole the rest of the way with soil, water it again and put down a layer of mulch.
• Keep the area wet for a few days.
• If the plant wilts in late evening or early morning, water again. And a little protection from the sun is a good idea, too.

Timing is important

• When dividing perennials, timing and technique are important.
• While many perennials can be divided in either early spring or early fall, some are very picky.
• The optimal time to divide specific perennials is denoted by (S) for spring and (F) for early fall.
• A single asterisk indicates that division should take place after the plant flowers.
• Two asterisks mean that protective gloves should be worn when dividing the plant, since its sap may irritate skin.

Divide these plants by hand

Blanket flowers (Gaillardia spp.) S/F
Bleeding hearts (Dicentra spp.) S*
Bugleweed (Ajuga reptans) S/F
Columbines (Aquilegia spp.) S/F
Coral bells (Heuchera spp.) S/F
Cranesbills (Geranium spp.) S/F
Creeping Jenny (Lysimachia nummularia) S/F
Deadnettle (Lamium maculatum) S/F
Epimediums (Epimedium spp.) S*/F
Foam flower (Tiarella cordifolia) S/F
Forget-me-not (Myosotis sylvatica) S*/F
Hellebores (Helleborus spp.) S*/F
Jacob’s ladder (Polemonium caeruleum) S/F
Lady’s mantle (Alchemilla mollis) S/F
Lamb’s ears (Stachys byzantina) S/F
Moss pink (Phlox subulata) F
Primroses (Primula spp.) S*
Pulmonarias (Pulmonaria spp.) S*/F
Pussytoes (Antennaria dioica) S/F
Sea thrift (Armeria maritima) S/F
Speedwell (Veronica spicata) S/F
Spurge (Euphorbia myrsinites) S/F**
Stonecrop (Sedum spectabile) S/F
Sweet woodruff (Galium odoratum) F
Violets, pansies (Viola spp.) S/F
Wormwood (Artemisia ludoviciana) S/F
Yarrow (Achillea millefolium) S/F

Cut up rhizomes and tubers with a knife on these plants

Arum (Arum italicum) F
Bergenia (Bergenia cordifolia) S/F
Caladiums (Caladium spp.) S
Calla lily (Zantedeschia aethiopica) S
Cannas (Canna spp.) S
Corydalis (Corydalis lutea) S/F
Dahlias (Dahlia cvs.) S
Elephant ears (Alocasia spp.) S
Irises (Iris spp.) F
Lady fern (Athyrium filix-femina) S/F
Lily-of-the-valley (Convallaria majalis) S/F
Rhubarb (Rheum palmatum) S
Rodgersia (Rodgersia pinnata) S/F
Spurge (Euphorbia griffithii) S/F**
Wild ginger (Asarum europaeum) S

Slice apart woody crowns with a handsaw on these plants

Amsonias (Amsonia spp.) S/F

Astilbes (Astilbe spp.) S/F
Bear’s breeches (Acanthus spinosus) S/F
Doll’s eyes (Actaea pachypoda) S
Foxtail lilies (Eremurus spp.) F
Gayfeather (Liatris spicata) S/F
Goatsbeard (Aruncus dioicus) S/F
Joe Pye weed (Eupatorium maculatum) S/F
Lilyturf (Liriope spicata) S/F
Male fern (Dryopteris filix-mas) S/F
Meadowsweets (Filipendula spp.) S/F
Peonies (Paeonia cvs.) F
Solomon’s seal (Polygonatum odoratum) S/F

Wild indigo (Baptisia australis) S*/F

 

Divide these plants with a spade or pitchfork

African lilies (Agapanthus cvs.) S/F
Anemone (Anemone × hybrida) S
Asters (Aster spp.) S
Bee balm (Monarda didyma) S/F
Bellflowers (Campanula spp.) S/F
Big bluestem grass (Andropogon gerardii) S/F
Black-eyed Susans (Rudbeckia spp.) S/F
Blood grass (Imperata cylindrica) S/F
Cardinal flower (Lobelia cardinalis) S/F
Catmint (Nepeta × faassenii) S/F
Coneflower (Echinacea purpurea) S/F
Daisy (Leucanthemum × superbum) S/F
Daylilies (Hemerocallis spp.) S/F
Forest grass (Hakenochloa macra) S/F
Fountain grass (Pennisetum alopecuroides) S/F
Garden phlox (Phlox paniculata) S/F
Gaura (Gaura lindheimeri) S/F
Goldenrods (Solidago spp.) S/F
Gunnera (Gunnera manicata) S/F
Hostas (Hosta spp.) S/F
Japanese painted fern (Athyrium niponicum ‘Pictum’) S/F
Jerusalem sage (Phlomis russeliana) S/F
Lemon balm (Melissa officinalis)
Ligularia (Ligularia dentata) S/F
Masterwort (Astrantia major) S/F
Monkshood (Aconitum napellus) S
Penstemons (Penstemon spp.) S/F
Perennial sage (Salvia × superba) S*/F
Pinks (Dianthus plumarius) S/F
Poppies (Papaver spp.) F
Red hot pokers (Knifophia spp.) S/F
Sedge (Carex morrowii) S/F
Siberian iris (Iris sibirica) F
Silver grasses (Miscanthus spp.) S/F
Snakeroot (Cimicifuga racemosa) S/F
Switch grass (Panicum virgatum) S/F
Tickseed (Coreopsis verticillata) S/F
Turtlehead (Chelone glabra) S/F
Yarrow (Achillea filipendulina) S/F

 

These perennials are best not divided

Alyssums (Alyssum spp.)
Candytuft (Iberis sempervirens)
Carnation (Dianthus caryophyllus)
Delphinium (Delphinium × elatum)
Euphorbia (Euphorbia characias ssp. wulfenii)
Foxgloves (Digitalis spp.)
Garden sage (Salvia officinalis)
Geraniums (Pelargonium spp.)
Lavender cotton (Santolina chamaecyparissus)
Lavenders (Lavandula spp.)
Rose campion (Lychnis coronaria)
Rosemary (Rosmarinus officinalis)
Russian sage (Perovskia atriplicifolia)
Sea hollies (Eryngium spp.)
Silvermound (Artemisia schmidtiana)
Sweet pea (Lathyrus latifolius)
Trillium (Trillium grandiflorum)

 

Happy Dividing & Transplanting