Dividing Perennials:
the easiest form of propagation
Linda Anson

Spring is in the air....

....and I start getting questions on just how and when to best divide those more expensive perennials. As they start reappearing in the garden, we avid gardeners look forward to seeing our "babies" grow up, and wish we could afford masses of them. Well, the truth is, we can. We just need to take advantage of Mother Nature’s growing methods to multiply the bounty.

Actually there are three reasons for dividing perennials: to control their size, to rejuvenate a plant, and for propagation. Most perennials will grow larger every year, usually by spreading into a larger clump. According to Ortho’s Complete Guide to Successful Gardening: "Left alone, the most vigorous growers can expand until they choke out many desirable plants. As the clumps expand, they also begin to compete with themselves; those plants on the outer edge thrive in fresh soil, but those in the center suffer from competition for moisture, nutrients, light and air. You can end up with a healthy circle of plants around a dying center." So, by dividing such a clump, you not only control the size if you need to in that particular spot, but you’re automatically rejuvenating the plant and creating potential new plants for use elsewhere in your garden (or your friend’s garden!)

A general rule of thumb for when to divide in our area is as follows:

• divide spring and summer flowering perennials in late summer/fall
• divide fall-blooming perennials in early spring

This gives the plants plenty of time to reestablish themselves. However, the truth is that in our area many perennials can be successfully divided throughout the growing season, within reason, of course. More critical than the precise timing of the division is the care with which it is done.

Ideally, you want to divide a plant when the soil is moist, such as after a nice rainfall. Lacking recent rain, thoroughly water the plant a day or two before starting the division work. You’re going to dig up the entire plant, and it’s critical to keep the roots from drying out, which can happen very quickly on a breezy and/or sunny day. It’s safest to immediately place the dug-up plant in a bucket of water, or at least under a moist cover while it’s waiting to be divided. (I personally try to wait for a drizzly or threatening day, when the soil is already moist, and the moisture in the air is sufficiently high to give me the time I need to divide and replant. Then I don’t have to bother with the water bucket. Usually this also means the temperatures aren’t so brutal for either me or the plant!) Then you can clean up the area you’ve dug up, removing any weeds, adding compost, and so on. For many perennials, after you’ve gently knocked off the excess soil (washing the soil off with a water hose works well), it will be relatively easy to tease the roots apart, either with your hands, or with a pair of spading forks, thus minimizing the damage to the root systems of both the new plants and the mother plant. However, for other plants, the roots are quite tangled, and you’ll need to carefully cut through the crown and the roots with a sharp knife or shears. Do not cut the new plants too small; you want to give them the best chance of survival by leaving enough root system. Don’t be too impatient: you’ll have another opportunity to divide in a year or two or three. For some plants, such as ornamental grasses, you’ll probably have to get more brutal and cut through the clump with a shovel. For one Miscanthus sinensis, I needed my husband’s help with a shovel to get through the mass!

Don’t try to divide the plant in place, take time to dig up the entire plant. Remember to keep the root system moist and as intact as possible. Then replant as carefully as you plant a new plant from the nursery, adding organic material to help the root system to reestablish itself more easily. (For an older mother plant, it might be best to discard it if it’s starting to struggle.) If the weather is hot, sunny, or windy the first days after replanting, it would be best to provide the new plants some cover protection, as well as ensuring plenty of water and, of course, mulch. The smaller the new plant, the more important the extra care.

If you’re new to dividing, try working with these more easily-divided common perennials: