Get Growing: How to divide your garden’s perennials 

  • A good rule of thumb for divisions is that they should be no larger than 20 or 25 percent of the total plant. MCT/Joe Fudge

  • Fall is the ideal time to divide perennials like daylilies and daisies, and to take cuttings of things like coleus. MCT/Joe Fudge

  • Most perennials enjoy being divided every few years. MCT/Joe Fudge

  • After perennials have their summer growing period, they create large root systems that can be divided up into several plants. MCT/Joe Fudge

  • After perennials have their summer growing period, they create large root systems that can be divided up into several plants. MCT/Joe Fudge

For the Gazette
Published: 9/6/2019 12:01:19 AM
Modified: 9/6/2019 12:01:09 AM

A friend recently told me that she was helping her daughter-in-law start a new perennial garden. She said she was hoping to divide some of her own perennials for her daughter’s garden and wondered whether it was too late in the year to do that. I was happy to tell her that September is an excellent time for this task.

Dividing plants in early fall means that temperatures are cooler and there are fewer biting insects. (Although I must note that our area is currently on high alert for mosquitoes bearing the dread EEE virus. See below for more information on this deadly virus.) The ground is likely to be moister, too.

Most perennials enjoy being divided every few years. They tend to get overcrowded in our gardens, which means that they have to compete with their neighbors for water and nutrients. They are also cramped for airflow, which makes them more susceptible to insect problems and diseases. Dividing promotes more vigorous growth. You can either replant divisions in other parts of your garden or give them away to friends and neighbors.

It’s easy enough to spot plants that have boundary issues. But even plants that aren’t crowded benefit from dividing every few years, when their growth habit has deteriorated. Signs of this include a bald spot in the middle of the plant, or smaller leaves and fewer flowers at the center. ‘Autumn Glory’ sedums often exhibit this problem.

Generally, it’s best not to disturb plants when they are flowering because at that time they are not able to put all their energy into growing a new root system. Some people make a practice of dividing spring and summer bloomers in the fall and waiting till spring to divide the late summer and fall bloomers. I have divided hardy souls like Rudbeckia and Epimedium when they’re still blooming, and they’ve survived happily.

Optimum digging and dividing requires some advance preparation. Plants do best when they’re well watered. Water thoroughly the day before, or at least a couple of hours prior to digging. If possible, choose a cloudy day that’s not too windy. Few of us can plan our gardening lives this strategically, but it’s worth keeping in mind.

Different plants have different types of root systems. Clumping plants, including hosta and echinacea, create offsets, or divisions. When you dig them up, you can see natural divisions with the root system below. When digging up an entire clumping plant, use a sharp, flat spade to dig straight down under the drip line of the plant (the outer periphery of its foliage). This is generally the extent of the root system. Work around the edge until you can gently ease the plant out of the ground. Pry these apart and save the strongest, healthiest sections. Each section should have 3 to 5 shoots and plenty of healthy roots.

Someone once told me that the best time to divide a plant is when it “looks good.” I tend to let plants get beyond this point, and there’s a price to be paid for this approach. I recently dug up some honker daylilies that had gone undivided for ten years or so. It took all the strength I had to get them out of the ground. I resorted to hacking them to pieces with my digging spade.

Plants with shallow roots that go along or just underneath the surface of the ground can be divided without digging up the whole plant. These include monarda and rudbeckia. Divide these by cutting between sections that have growth shoots and roots. Similarly, plants with underground running roots generate suckers that grow off the main plant. These include hardy geraniums and anemones. Suckers can be removed and replanted without disturbing the mother plant.

Plants with woody roots, like astilbe and lavender, form when a woody part of the plant rests just above the ground. Dig up the whole plant and cut off healthy divisions with pruners or a hand saw.

The most difficult plants to divide are those with taproots, including peonies and asclepius. Some garden experts advise against dividing these. If you do divide them, wait until fall and gently dig up the entire root, making sure you don’t break it. Then, with a sharp knife, slice off a piece of the root that contains at least one eye and several side roots. When replanting, make sure the eyes are only 2 or 3 inches beneath the surface.

A good rule of thumb for divisions is that they should be no larger than 20 or 25 percent of the total plant. Smaller divisions are happier and last longer before they need further dividing. Each division should have three to five healthy shoots and a good amount of roots. When dividing plants that have weak centers, take divisions from the outside edges of the plant and toss the woody, failing central part.

If you can’t replant your divisions right away, save them in a shady place—a garage or shed is ideal—under damp newspapers. If you’re giving them to friends, put them in old plastic flower pots you’ve probably got stacked by the dozens. Add a generous amount of compost and keep them moist. Your efforts might bring you a return gift in the same pot! If you’re replanting the divisions in your own garden, avoid the temptation to simply stick them in the ground and call it a day. Add compost to your empty hole and place each division carefully so that its roots are spread and pointed down. Don’t cram the roots into too small a hole so that the roots are bent back and up. I confess this is easier said than done sometimes when you’re running out of time and your lower back is shouting, “Enough!” But the more care you use at this point, the happier and healthier your new plants will be next season.

Water the replants well and mulch them to retain moisture and retard weeds. Pay attention to the weather and water the plants well into the fall as needed. We’re likely to have hot, dry spells throughout September and October.

Digging and dividing is one of my favorite gardening tasks. Novice gardeners may find the prospect daunting, but they will happily discover that plants are very forgiving. I can’t begin to count all the veteran gardeners who have assured me over the years that plants love to be divided. And they’re right.

Mickey Rathbun, an Amherst-based lawyer turned journalist, has written the Get Growing column since 2016.Fall programs atthe Hitchcock Center

Hitchcock Center’s fall programs for children and families are starting soon, including Girls Into the Wild! and Nature Preschool Discovery sessions. The Saturday Family Science Series will kick off at the center’s Pollinator Celebration on Sept. 14 from 10 a.m. to 2 p.m. This is a ticketed event. For information about all programs, including dates, times and availability, check the website, hitchcockcenter.org.

Bringing plants indoors

On Sept. 14 from 10 a.m. to 1 p.m., Berkshire Botanical Garden in Stockbridge is hosting a class on strategies for bringing outdoor plants including tender perennials, potted woody specimens and succulents inside and keeping them thriving through the winter. The class will include tips on fertilizing, watering, cultivating and overall plant health. Instructor Jenna O’Brien is the owner and founder of Viridissima Horticulture and Design, in business since 2003.

EEE alert

Several cases of Eastern Equine Encephalitis (EEE) virus, a serious, often fatal, mosquito-borne disease, have been reported in Massachusetts. One involved a horse in Granby, according to state health officials. The state has raised the EEE risk to critical in Granby and high in South Hadley and Belchertown. High risk means that conditions are likely to lead to EEE infecting a person. Critical means there is “excessive” risk or that an infection has already been confirmed in an area. According to the Centers for Disease Control and Prevention, only 4 or 5 percent of people infected with the virus contract the disease, but about one-third of the people who contract EEE die, and others are likely to suffer brain damage. Early symptoms include headache, high fever, vomiting and chills.

As far as I know, mosquitoes don’t observe municipal boundaries. The peak time for mosquito-borne illnesses lasts through September. So play it safe, even if you don’t live in one of the high or critical alert towns. Use mosquito repellent, wear long pants and long sleeves and stay inside after dusk. Empty any containers of standing water; refill birdbaths daily.




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