Dividing is the process of lifting an established perennial out of the ground, loosening or cutting the root system and making more plants from one. While it may sound like plant abuse or a primitive form of cloning, the process is beneficial on many levels. Division helps control the plant’s size, peps up the plant, and creates more plants.
Think of division as harvesting new perennials from your garden. It’s nature’s bonus plant program. With these freebies, you can expand your garden or create masses for added impact. Expand friendships by gifting bonus plants.
There are just a few things to consider. Different perennials like to be divided at different times and there are some that just don’t like it much. Bloom times can help you figure out when to divide which plant.
“If it blooms in the spring, divide in the fall. If it blooms in the fall, divide in the spring,” said Horticulturalist and perennial plant guru Wendy Brister; “However, in the spring, right as everything is just emerging is usually a safe time to divide most things.”
Early in the spring, there is less foliage for the plant to support and continued mild and moist spring conditions give the root system time to grow before the plant is stressed by heat or periods of drought. Fall offers similar conditions. Just make sure to divide about four weeks before the first hard frost so the root system has time to rebuild before winter.
“The great thing about perennials is if you HAVE to, you can divide any time of year and they are pretty resilient. They may just go into early dormancy but they
should bounce back by the following year,” said Brister.
There are a few plants that like to stay put.
“Perennials with a taproot don't divide well. Baptisia australis, False Indigo, is a big one. Asclepias tuberosa, Butterfly Weed, doesn't divide well either. For those types, wait till you get some seedlings and move the babies,” said Brister.
Seedlings transplant better because the taproot has not had time to develop. A taproot is a vertical and deep growing root. Poppies and thistle, for example, get grumpy about moving due to their long taproots. Again, not to worry. Plants really want to survive, so if you lift a plant and find it has a long taproot, just replant it. Keep it watered until the plant has re-established and chances are, the plant will be just fine.
While some plants are homebodies, others like to roam. If you notice that after a few years, a perennial is not blooming well or you begin to notice that the center of a clump is dying out, those plants need to travel. Dividing rejuvenates many plants.
“In my experience, it’s important to divide daylilies. They tend to bloom less
when the clump gets too big,” said Brister, “Some plants, like Rudbeckia, tend to die out in the center after a couple years.”
Iris is another plant that likes to be on the go. They like to be divided after they bloom in the summer and into early fall. Iris roots are rhizomes and they spread by growing new rhizomes. To divide Iris, cut back the leaves to several inches tall, lift the plants, then use a sharp knife to cut the new plants from the older plants. Often you will see new leaves on the baby rhizomes. You can discard the old rhizomes. Shallowly replant the smaller rhizomes.
Iris can stop blooming if not divided routinely. Most perennials can be divided every two to three years.
“Usually, the plants let you know when they need to be divided,” said Brister, “OR if your friends want some of your plants, then divide away!”
Healthy plants do their best to stick around. Handle your plants. Move them around. They will reward you by growing beautifully.