Dividing Perennials

With the cooler weather upon us, we are all thinking about putting our gardens to bed for the winter, enjoying the coming holidays, and then anxiously awaiting the reawakening that Springtime will bring. Before we turn off the lights and tell our plants to take a nice long winter rest, we should think about dividing some of our perennials so that with room to spread we will continue to enjoy them throughout our gardens for years to come.

Most of the perennials that grow well here in the Sandhills can be divided in late autumn or early spring but regardless of when you divide, there are some simple, basic rules you should follow.

• DIVIDE WHEN THE PLANT IS HEALTHY - Don’t wait until it is overgrown or cramped in its current space, or when the center has smaller leaves, fewer flowers or weaker drip line, if you begin by lifting the plant there you will minimize root damage. Dig a trench around the clump of the plant, severing any extended roots cleanly and then cut down and under the clump so that you can lift the plant intact. If you are dividing your plants in the Fall, cut them back before digging them up for dividing. If in the Spring, divide while the new growth is still new to the ground.

• START DIVIDING AT THE DRIP LINE - Since perennials roots generally extend to the drip line, if you begin by lifting the plant there you will minimize root damage. Dig a trench around the clump of the plant, severing any extended roots cleanly and then cut down and under the clump so that you can lift the plant intact. If you are dividing your plants in the Fall, cut them back before digging them up for dividing. If in the Spring, divide while the new growth is still new to the ground.

• DIVIDE IN COOL WEATHER - It doesn’t matter if you choose to divide in the Spring or Fall, so long as you consider the air and soil temperature carefully to give the divided plants have the best chance of reestablishing themselves successfully. It’s always best to divide when the soil is warmer than the air for at least part of every 24 hour period. If you divide in the Fall, your plants will have a bit more time to set new roots before facing the heat of our Carolina summers.

KEEP THE ROOTS COOL AND MOIST - If you can’t immediately get your divisions back into the ground, put them into a bucket or box in a cool shaded place and cover them with newspaper to prevent moisture loss. If, however, your divisions dry out before you can replant them, simply soak them in a bucket of water for about an hour before replanting

• REPLENISH THE SOIL BEFORE REPLANTING - Before replanting your divided perennials, always put an equal amount of composted organic materials back into the site where you removed first removed them. This is especially important here in the Sandhills where our soil tends to need amendment regularly.

• REPLANT SMALL 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.

• KEEP ONLY HEALTHY DIVIDED PIECES FOR REPLANTING - Be sure that you don’t wait until a plant is declining, has a dead center, or has succumbed to pest problems before you divide and replant it. If you divide a diseased plant and replant anything but a healthy section, all you will be doing is ensuring that all new shoots and buds will be exposed to the infection. One of my most favorite perennials are peonies and I take special care with those of my older plants that I had successfully moved here from New Jersey a few years ago. I never wait for my peonies to become crowded before dividing them – crowded peonies are weak peonies and become susceptible to pest problems and disease. I routinely divide and replant them around my garden, making sure I do not use discolored stems or eroded crowns and roots. With a little care I am enjoying these fabulous plants and their offspring throughout my yard.

• SPREAD OUT YOUR DIVISIONS - Replant divisions in a wide hole and over a wide area making sure the division is planted into a hole that is at least as wide as the roots when they are spread out. If done carefully in the next growing season, the top of the plant will be as wide as the roots are at the time of planting. Also make sure you don’t turn the root tip up instead of placing it down and don’t force your division into an undersized hole thereby curling the roots back onto themselves. As we all should remember from our MGV classes, root tip growth is impacted by chemicals flowing down from the tips of leafy stems to the roots. Don’t mess this up!

• PAY ATTENTION TO YOUR PERENNIALS ROOT TYPE - You will have to proceed slightly differently depending on whether your perennial has roots that form clumps or offsets, surface roots, underground running roots, taproots or woody roots.

• 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.

* Surface Roots:If the roots of your perennials run on or just below the surface of the soil, they form new crowns and roots when they reach open space or make contact with the soil. Cut between any of those stems and you will have a division with its own stems and roots and one that is sure to reestablish itself successfully.

• If your perennial has taproots, divide it by using a sharp knife to slice down the length or the taproot. If your division has at least one eye, a bit of the taproot and a few side roots, it will be viable.

* Underground Running Roots:Those plants that have underground running roots tend to develop suckers as they grow beyond the shade of the mother clump. To divide perennials with underground running roots you can cut away the suckers from the mother plant or dig up the mother plant and cut away any piece with a sucker already forming.

* 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.

Following is a list of some of the perennials native to North Carolina, with an indication of whether they are to be divided by hand, divided with a spade or pitchfork, sliced apart with a handsaw or not divided at all.Most can be divided in either the Spring or early Fall, but those that can only be divided in a particular season are denoted by (S) for spring or (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.)

Bleeding hearts (Dicentra spp.) S*

Bugleweed (Ajuga reptans)

Columbines (Aquilegia spp.)

Coral bells (Heuchera spp.)

Cranesbills (Geranium spp.)

Deadnettle (Lamium maculatum)

Foam flower (Tiarella cordifolia)

Hellebores (Helleborus spp.) S*/F

Jacob's ladder (Polemonium caeruleum)

Lady's mantle (Alchemilla mollis)

Lamb's ears (Stachys byzantina)

Primroses (Primula spp.) S*

Pulmonarias (Pulmonaria spp.) S*/F

Sea thrift (Armeria maritima)

Speedwell (Veronica spicata)

Spurge (Euphorbia myrsinites) S/F**

Stonecrop (Sedum spectabile)

Violets, pansies (Viola spp.)

Wormwood (Artemisia Absinthium)

Yarrow (Achillea millefolium)

Divide these plants with a spade or pitchfork

African lilies (Agapanthus cvs.)

Anemone (Anemone × hybrida) S

Asters (Aster spp.) S

Bee balm (Monarda didyma)

Bellflowers (Campanula spp.)

Black-eyed Susans (Rudbeckia spp.)

Cardinal flower (Lobelia cardinalis)

Catmint (Nepeta × faassenii)

Coneflower (Echinacea purpurea)

Daylilies (Hemerocallis spp.)

Garden phlox (Phlox paniculata)

Gaura (Gaura lindheimeri)

Goldenrods (Solidago spp.)

Hostas (Hosta spp.)

Monkshood (Aconitum napellus) S

Penstemons (Penstemon spp.)

Pinks (Dianthus plumarius)

Poppies (Papaver spp.) F

Tickseed (Coreopsis verticillata)

Slice apart woody crowns with a handsaw

Amsonias (Amsonia spp.)

Astilbes (Astilbe spp.)

Bear's breeches (Acanthus spinosus)

Foxtail lilies (Eremurus spp.) F

Gayfeather (Liatris spicata)

Meadowsweets (Filipendula spp.)

Peonies (Paeonia cvs.) F

Solomon's seal (Polygonatum Biflorum)

Wild indigo (Baptisia australis) S*/F

Cut up rhizomes and tubers with a knife

Calla Lily (Zantedeschia aethiopica) S

Cannas (Canna spp.) S

Dahlias (Dahlia cvs.) S

Irises (Iris spp.) F

Lily-of-the-valley (Convallaria majalis)

Rodgersia (Rodgersia pinnata)

Spurge (Euphorbia griffithii) S/F**

Wild ginger (Asarum europaeum) S

These perennials are best not divided

Candytuft (Iberis sempervirens)

Carnation (Dianthus caryophyllus)

Delphinium (Delphinium × elatum)

Foxgloves (Digitalis spp.)

Lavenders (Lavandula spp.)

Rose campion (Lychnis coronaria)

Russian sage (Perovskia atriplicifolia)

Sea hollies (Eryngium spp.)