Dividing Perennials: The Long and Short on Divisions
As the summer sun sets on the tired and weather beaten landscapes of Louisiana, perennials across the state yawn at the thought of toiling another day. The lackluster foliage of ornamental grasses and agapanthus flops half-heartedly to the ground, and the once cheery-eyed faces of daylilies, Acanthus mollis, and Echinacea now smile with forced efforts and waning vitality. Some perennials like hostas and calla lilies have given up completely, seeking cooler repose beneath the soil surface.
Although your perennials may be contemplating early retirement this fall, don’t let them rest without putting up an extra fight. With plenty more warm days ahead, this is the perfect time to get more bang for your buck from any of your perennial favorites. Dividing herbaceous perennials is an easy and often necessary chore that can be done in late summer and early fall to help revitalize jaded plants, as well as double your number of returning companions.
Defining the Task
Herbaceous perennials, simply put, are plants that bloom year after year. Their foliage dies back to the ground each fall, but their crowns and root systems remain alive throughout the winter. They hibernate, in other words, beneath the earth’s soil so as to regain strength from their crowns and roots. Each spring they loyally return, their lush foliage and blooms packed with renewed vigor and brighter colors for the seasons ahead.
The Dig on Divisions
If you garden with perennials, then it is no secret that after a few years they begin to decline. Their flowers don’t open quite as fully or as often as they once did, their growth appears somewhat sluggish and spindly, and the centers of the plants show no signs of growth, leaving behind empty voids with faded green perimeters. Rather than replacing your weary perennials though, delve into the depths of their splendor through divisions. Dividing herbaceous perennials not only allows you to control the size of your plants, but it helps your perennials to retain their youthful vigor as well. By dividing your perennials, you ultimately acquire more of your favorite flowers over time—you can replant your treasured beauties to fill other spots in your garden, or offer them to family members and neighbors who share the same love of flowers as you. The best gardeners after all, never let their plants go to waste.
Keep in mind that there is no set rule as to when you divide perennials. Daylilies, asters, and salvias for instance, prefer to be divided every two to three years, while perennials like agapanthus and hostas can be left undisturbed for five to seven years. Still others like butterfly weed (Asclepias tuberosa), columbine (Aquilegia spp.), and false indigo (Baptisia australis) would not be bothered at all; with these perennials, propagation by seed is the preferred method. For the most part, perennials can be divided when they are inactive, either in early spring before they break dormancy, or in the fall so that the roots of the new plants can get settled in before the ground freezes.
Playing Spades
Dividing perennials can often prove an easy feat, but depending on the type or age of the plant, you may need the help of a shovel, spading fork, or pick. Begin by digging the entire plant from the ground. Wash or break any excess soil from the roots, and then cut or pull apart the clump into several pieces, making sure not to cut through crowns or damage shoots; each new plant should be about the size of a one gallon perennial. Agapanthus and young gingers or irises are often easy to separate with your hands, while ornamental grasses, Cyperus, and aspidistra require back-up assistance from spades or shovels. If you divide your plants in the fall, take some extra time to spruce them up as well. Focus on preserving the newer leaves and roots, while discarding any old, damaged, or diseased growth. Replant the divisions into a larger area than the plant once occupied, using a garden soil rich in organic matter, and water well to protect the roots from drying out.
Perennial Care for the Fall
In autumn, cut back most perennials to about three inches from the ground (any closer may damage crowns), and remove any debris from flowerbeds to help prevent diseases. Some perennials such as ornamental grasses, European gingers (Asarum spp.), and upright sedums prefer to be cut back in early spring. Add a protective layer of mulch—one to two inches thick—after we have had a few severe frosts and the soil has cooled, usually mid to late October in Louisiana. Take care not to apply the mulch too early, since it will retain heat in the soil, causing some plants to break dormancy and start growing again. Gradually remove some of the mulch in the spring as the perennials start to awaken.
Perennial Tip
Some herbaceous perennials will flourish only if you dig them up every few years and divide the root systems. Each time you do, you turn what was once a single plant into several new plants you can replant or share. ✦
Basic Division Chart
Acanthus mollis
divide every 3 or 4 years in late summer/fall
Agapanthus (Lily of the Nile)
every 4 or 5 years in late summer/fall
Aster (Aster spp.)
every 2 or 3 years in spring
Astilbe (Astilbe spp.)
every 3 or 4 years in spring
Bee balm (Monarda didyma)
every third year in spring
Bleeding heart (Dicentra spp.)
division is difficult; best done in late summer/fall
Chrysanthemum
every 2 or 3 years in spring
Coral bells (Heuchera spp.)
divide in late summer/fall
Cyperus
divide in late summer/fall
Daylily (Hemerocallis spp.)
late summer/fall
Gingers
every 3 to 5 years in late summer/fall
Hosta (Hosta spp.)
plants can be left undisturbed for years; divide in late summer/fall if necessary
Indigo
late summer
Iris, bearded
every 3 to 4 years in July or August
Iris, Louisiana hybrids
late summer/fall
Ornamental grasses
early spring or late summer/fall
Salvia (Salvia spp.)
early spring
