by Andrea Laine EMGV
There’s a saying among gardeners: Sleep, creep, leap.
The first year that an ornamental plant is in the ground, it sleeps. Above ground it looks like nothing is happening. All the action is underground where it is creating strong roots. A quality root system is essential for absorbing water and nutrients to deliver to the rest of the plant.
The following year, the plant creeps. We may notice new leaf buds, an elongated stem, and we are content (or relieved) that the plant is still living.
Then, finally, in its third or fourth year, the plant really starts to get showy. It leaps! There are new leaves and bold flowers. The plant is noticeably taller and/or wider and we gardeners are filled with pride and joy and our enthusiasm for gardening probably leaps, too.
This is so true of herbaceous perennials! Before you know it, it is time to divide the perennial into smaller plants. Division can control a plant’s size and invigorate the original plant, assuring that it continues to flower abundantly. (If your perennial no longer flowers very well, that is a sure sign that it is crowded and needs to be divided.) Another benefit is that you will have new plants to place in another part of the garden or share with a friend or neighbor.
Time of year
The best time to divide herbaceous perennials is early spring, however bearded iris and Asiatic lilies prefer later summer to early fall and some plants like black-eyed Susan are so resilient they’ll accept division in spring or fall. Choose a cool or cloudy spring day or an early fall day. Dividing or planting most perennials during a hot and/or humid day, such as we tend to have during a Durham summer, is generally not advised. Also, do not divide or dig around plants the same day they have been watered.
Step-by-step guide
Step 1. Prepare by putting in place everything you may need to complete the task: a long-handled spade or digging pitchfork, a sharp knife (I use an old steak knife from the kitchen), a full watering can or hose, and newly dug holes in the ground. If you intend to gift your divisions to other gardeners, then also have containers, a small spade and potting soil by your side.
Step 2. Survey your plant(s). From afar, it looked like I had two giant clumps of Stokes Aster (Stokesia ‘Peachies Pink’). See photos below. They had been in the ground four years. But upon closer inspection, notice that there are actually multiple small clumps growing close together.
Step 3. Dig and separate the plant. Use the spade or fork to dig deep on all four sides of the plant. In the case of these asters, I need not dig up the whole planting, just the smaller clumps that I wish to relocate. If the plant’s divisions are growing closely together, as may be the case with a Daylily or a Bearded Iris, you may need to dig up more, or all, of the plant. When that is the case, gently pull the division away from the original plant. Tease it with your fingers. If this is difficult, as it may be with plants that are overdue for dividing, it’s okay to cut through the clump using the knife. Just be sure that each smaller clump gets three to five shoots and part of the root system.
Step 4. Replant the divisions, with proper spacing and depth (the crown at soil level), as soon as possible into your previously dug holes or at-the-ready containers. The goal is to minimize the amount of time that the roots are exposed to the drying effects of air. Water the new planting well.
As you can see in the photos above, the new divisions look a bit forlorn 10 days later. They will need nurturing equivalent to any new planting; that means vigilant watering through their first year. It is also helpful to snip new flower buds off the first year or two, if any even develop, so the plant’s energy can be concentrated on developing its root system. Remember: sleep, creep, leap!
Step 5. Pay attention to the original plant. Rebury its roots if any were exposed during the division. Enrich the soil with compost or soil conditioner. Even just loosening it will help; Plants dislike growing in compacted soil. Having some garden soil or compost on hand is helpful but not necessary. It’s okay to add the compost later in the growing year when social-distancing may not be as critical as it is this spring.
Follow similar five steps if you wish to relocate a plant: Prepare, survey, dig, replant, nurture. I divided the asters last spring and the new plants are doing very well. I will divide and move some hostas to shadier places this year. My landscape has changed (we took down some larger trees) and the hostas are no longer planted in the right place for their needs.
Early spring days are excellent for separating, dividing or relocating perennials. And, these are tasks you can accomplish with equipment and material already on hand. Perfect for gardeners sheltering-in-place.
1Perennials not recommended for division
- Baby’s Breath (Gypsophila)
- False Indigo (Baptisia)
- Balloon Flower (Platydocon)
- Flax (Linum)
- Bugbane (Cimicifuga)
- Lupine (Lupinus)
- Butterfly Weed (Asclepias)
- Monkshood (Aconitum)
- Clematis
- Russian Sage (Perovskia)
- Poppy
Divide Only to Propagate
- Bugbane (Cimicifuga)
- Tall Sedum (Sedum “Autumn Joy“)
- Garden Peony (Paeonia)
- Yucca
- Red-Hot Poker (Kniphofia)
Resources
1. Some plants need dividing more often than others. Scroll to the bottom of this link for a list of perennials and their division requirements.
https://extension.psu.edu/dividing-perennials
http://chemung.cce.cornell.edu/resources/dividing-perennials
Further Reading
A glossary of gardening terms
https://content.ces.ncsu.edu/extension-gardener-handbook/glossary
The many ways to propagate plants are described in the Extension Master Gardener Handbook: https://content.ces.ncsu.edu/extension-gardener-handbook/13-propagation#section_heading_5641