How to Split Perennials

Perennials are one of my favorite topics to teach people about—why? Because you plant them once and you’ll have them forever! Well, technically a perennial plant is a plant that lives for at least 3 years…but many perennial plants can live for decades.

What’s perennial in your area depends on your grow zone. For example, plants that are perennial in my zone of 7 might not be perennial in zone 4, which is colder and farther north. So know what’s perennial in your area, plant it, and enjoy it for years 🙂

Why split perennials?

Because perennials will come back year after year, you’ll probably have to eventually split them by digging them up and replanting only a portion of the plant. Or you can just dig up part of the plant to contain its spread.

Different perennial plants spread with different levels of aggressiveness. For example, my aromatic aster is on its 4th year and is starting to spread pretty aggressively. Clustered mountain mint, another one of my favorite perennials, also tends to spread readily.

But other perennials don’t seem to spread as aggressively in my yard. For example, while my coneflowers have tended to mound and fill out nicely after a few years, they haven’t required me to do any downsizing just yet.

Plants can also get overcrowded with time. Their centers may thin out, or they might stop blooming as much. Splitting gives them room to breathe, helps them absorb nutrients better, and encourages fresh growth. Plus, you can turn one plant into multiple plants! 🙂

Dividing perennials

Dividing perennials just means digging up a mature plant and splitting it into smaller sections—each one with roots and growth points. Or it can mean just digging up a portion of the plant, making sure to take some roots and growth points with it when you dig.

Most perennials are best divided in early spring or early fall—when the weather is cool and the plant is either just waking up or winding down. I like to avoid digging up perennials in the summer because they can get quite large and unruly…plus the intense summer heat can make transplant shock worse.

You don’t need much. Just a shovel and maybe a sharp knife or pruning saw for tough roots. I like to use my hori-hori knife. I also like to wait until it has just rained to split perennials. That way you know the plant is well hydrated and the soil will be easier to dig into.

To divide a smaller plant, you can dig up the whole things and break apart the plant at the root level. If your plant is larger like the aromatic aster I’m digging up here, you can dig up in smaller sections. Regardless of the method you choose, don’t worry about breaking roots and leaves. The plant will rebound just fine!

Replant the sections of the plant you’ve separated or dug up into pots with some fresh potting mix. I like to keep some of the native soil and mix in a bit of leaf compost. Then water deeply. Make sure to keep the plant moist, especially since they are in smaller containers that don’t retain water as well as the ground does!

If you want to skip the potting step all together and plant the transplant directly into a different spot in your garden, that’s even better! I usually throw in a handful or two of fresh compost when planting and still make sure to water deeply. But water retention is much better for plants in the ground.