One of the easiest ways to propagate perennials is to divide the crowns at the end or beginning of the growing season. The general rule is that you divide summer and fall-blooming species in the late winter/early spring and spring blooming plants in fall. There are always exceptions to the rule, and some plants just don’t divide, so do a little research on your specific plant before you start the division process.
First, a vocabulary lesson: Plant crown – the part of the plant where the roots meet the stem, most often at or near ground level. It logically follows that your plant must have multiple crowns in order to divide them from one another. Most perennials will grow large enough to sprout multiple crowns within 3-4 years of the initial planting. Some will start to spread outward and may need to be divided in order to contain their growth and maintain your gardens aesthetic. Newly divided crowns can be used to start new beds, given to friends and neighbors, or simply moved a few feet away to establish a larger colony and give everyone more room to grow.
Here’s a photo walk through of the process using a 3 year old Alumroot (Heuchera americana) :
It’s been in this pot for far too long, but has made the most of it by sprouting multiple crowns.
First step is to remove the plant and as much of its roots as possible from the container/ground:
If you want to divide a plant that is already in the ground, just dig out the surrounding soil (gently) and try to get as much of the root mass as possible. You will inevitably have to cut/break some roots, but as long as you get the bulk of them it should be fine.
Gently remove the soil from the roots and tease them out slowly. You might be surprised just how long they are. These were at least twice as long as the depth of the pot they were in:
Now that most of the soil is removed, a little water can help to take the rest out of the roots, and make sure that the roots are nice and moist and pliable so they don’t break easily as you separate them. I usually dunk the whole thing in a half-filled bucket and swish it around a bit.
Here is the same plant after a dunk, and you can now clearly see the roots without the soil. I’ve used arrows to point out the two separate crowns now visible in the mass of tangled roots. There’s one more smaller one hiding in the background as well. The goal is to get all three of these crowns separated from one another while minimizing the amount of root breakage. It’s a lot like untangling hair, it takes a little patience and finesse.
They are starting to come apart, and now we can see all three crowns. I find I have the best success when I gently pull the crowns apart in opposing circular motions. I often will do that in the bucket with the roots underwater, as it seems to help the roots slide apart instead of break.
Here are the three crowns fully separated and ready to grow into three independent plants.
When replanting (in a pot or in the ground) make sure that the crowns are at the same height in relation to the soil as they were before division. Too high and the roots will dry out; too low and the stems will rot. Make sure they’re just the right level so that they’ll grow prolifically for the next few years and give you a whole new batch of crowns to divide.