The fall garden brings a multitude of projects and tasks, some quite satisfying and others just things to get done. But one of those projects can make tremendous contributions to next year’s garden — dividing your herbaceous perennials. Perennial division is easy street to new (free?) plants for the garden. It can also be an essential part of keeping a prized plant healthy and vigorous.
First — a little plant terminology. A perennial plant is one that is programmed to grow year after year (as opposed to an annual plant that completes its full lifecycle in one growing season.) A herbaceous perennial typically sheds its top growth in fall and overwinters as a fleshy storage organ below ground. That overwintering mass sends up new growth in spring. Trees and shrubs are considered woody perennials — plants that retain an above ground portion through the winter.
In our constant effort to confuse non, or new gardeners, most plantfolk use the shorthand word, perennial, to refer only to herbaceous perennials. Trees and shrubs fall under the category of, woodies. Don’t sue me. I didn’t make it up.
With that out of the way, let’s talk perennial division.
What is a herbaceous perennial?
The underground, overwintering part of a herbaceous perennial can come in a variety of flavors. There are bulbs (tulip), cormbs (crocus), tubers (peony), and rhizomes (iris), among others. But all fall into a similar pattern. They all have fleshy parts that store energy, water, and nutrients for the following season. There are fine roots that usually emanate from the base of the fleshy part. In most herbaceous perennials, those fine roots are produced in spring, absorb water and nutrients from the soil all summer, and die off in fall. Then there are vegetative buds (often called eyes) that produce the following season’s leaves and flowers.
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As a perennial plant grows and matures, the fleshy portion tends to get larger each year, and in most types as it enlarges the mass produces additional eyes. Some plants may take multiple years to go from one eye to two (I have one as-yet-unidentified Asian Solomon seal that hasn’t produced a second eye in eight or nine years!) Others might jump from one eye to 10 or 15 in a single season. If you ever wondered why that favorite hosta or daylily you’ve been eyeing in catalogs is so much more expensive than the others, it might just be that it is a slow multiplier so takes longer for growers to make more stock to sell.
How to divide herbaceous perennials
Now in a giant twist of good fortune, Mother Nature has done gardeners a solid by arranging this whole system in a very convenient way. In most cases, you can dig up a perennial and cut that fleshy part into smaller parts, and as long as each of those bits contains sufficient fleshy mass and a single eye, it can be planted and will grow into a new plant.
It can be a little intimidating and/or confusing to start hacking away on your prized peony if you’ve never done it before. How do I identify an eye? What’s enough root? Can I really just hack these things into pieces? Aren’t they quite fragile things? All reasonable questions.
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The nice thing about fall division is that you typically still have some foliage hanging around and that can be helpful in identifying a perennial’s eyes. Simply dig up your plant clump and shake off as much soil as possible. (Don’t worry. They’re nowhere near as fragile as you might think. And the fading, yellowing fall leaves aren’t providing much, if anything to the plant by this time of year.) You can even take a hose sprayer to wash away stubborn soil so you can see what you’re doing. Once cleaned up a bit, you can typically see clumps of foliage growing from one or more eyes.
Once you locate the eyes, all that’s left to do is to slice and dice. To cut the mass apart you can use a sharp garden spade, soil knife or just about anything else that has a sharp and sturdy edge. I have one nursery friend who has found his favorite division tool to be a hack saw. Seems to work fine for him.
If your goal is to make as many new plants as possible, you might want to divide your plant into single eye divisions. They’ll be small next year but will eventually grow and mature. But if you have one nice big hosta, and you want a matching partner for the other side of the path, you might want to simply dig up the plant and divide it in half. You’ll only increase from one hosta to two, but they’ll both be bigger plants next year. Dealer’s choice.
How often should you divide your plants?
One last point about dividing perennials is that it’s not always all about making more plants. Sometimes it’s about keeping your plant healthy and vigorous. Some herbaceous perennials, including many ornamental grasses, have the tendency to die out in the center as the plant grows and matures over several seasons. To avoid this, you can divide your plant every few years. If you have a plant that’s already showing a bald center, you can simply divide out and replant the portions that show good growth.
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Like everything in gardening, it takes a little practice, and you’ll likely lose a division or two along the way. But once you get the hang of it, you’ll find yourself with more plants than you know what to do with. The good thing is there’s always room for a few more plants, and if you do run out of room, there’s always a garden friend who will be happy to give them a home.
Paul Cappiello is the executive director at Yew Dell Botanical Gardens, 6220 Old Lagrange Road, yewdellgardens.org.
This article originally appeared on Louisville Courier Journal: How and when to divide herbaceous perennials. What to know