Colorado gardening: Dividing perennials equals multiple plants

What’s the one spring garden chore that costs you nothing, and yet earns you free plants?

If you answered dividing perennials, then give yourself a nice pat and keep moving. It’s go-time with your shovel.

Simply said, dividing a plant into two or more vegetative pieces or clumps is the best way to stimulate new root growth for plants that are no longer growing and blooming with vigor like they previously have.

Sometimes, plants poop out in the center (ornamental grasses, I’m talking to you). Plants can also crowd out surrounding plants or outgrow their zip code and spread to Kansas (culinary mint comes to mind).

Try as we might when gardening, sometimes we plant perennials in a landscape location that just isn’t suited to the growing conditions they prefer. They might need more sun or shade or less root competition. Move the plants this spring where they’ll be happier; just follow the same directions below but skip the division steps.

When to divide

An easy-to-remember rule of thumb is to divide fall-blooming perennials in the spring and spring bloomers in the fall. Mid-summer bloomers can be divided in either spring or fall.

As days lengthen and soil warms up in the spring, the newly divided plant’s roots will take off and you’ll practically never know it was tampered with. The same goes for fall division when the plant is focused on root growth since it already bloomed in the spring. Divide plants in the fall a good six weeks before frost is predicted. They need time to settle in before the soil freezes.

Try to avoid dividing in the heat of summer; the exception is bearded iris, which mostly go dormant in the summer and prefer being divided after blooming (July-August).

How often to divide is up to you and the plant; some experts say every three to five years or longer. Try to divide before you see the plant going downhill. It’s OK to divide a plant that’s thriving and healthy if you know it will need it eventually.

The goal is to divide plants when you see new growth starting in the spring. Early spring through mid-May is the sweet spot. Soil conditions matter, too: The soil shouldn’t be too wet or frozen.

How to divide in spring

First, determine your plant’s root system type. Learning the way the plant roots grow will help with the right procedures to divide (types described below).

Water the plants to be divided a day or two prior to dividing if it’s been dry. Choose a cloudy day; if rain is expected after completion, that’s a bonus.