What is a Perennial?
Perennials, by definition, are plants that live more than two years. Some perennials, like peonies, live for decades; others like gaura, live three to five years. Ballon flowers or Platycodon grandiflorous, live 20 years or more without needing division. Each plant is different, and some, like black-eyed Susan, reseed everywhere in the garden, extending their lifespan for as long as you want.
Perennials are also loosely defined as anything that doesn’t have a woody structure, such as herbaceous perennials. Though, technically, trees and shrubs are perennials, too.
Why Divide Perennials?
Many new (and not-so-new) gardeners think of perennials as one-and-done plants. Not so! Perennials provide years of beauty to our gardens, but do require some maintenance. Division is a primary task associated with perennials, but do you know why we divide perennials?
- Perennials can get too big for their spaces (like the hosta pictured), crowding other plants.
- Division helps avoid fungal diseases and supports pest control as it allows for better air and sunlight circulation.
- The center of the plants can start to “bleed out,” forming a sort of donut hole in the middle.
- Perennials start producing fewer flowers, or have straggly-looking leaves, or weak growth. (This could also be a sunlight issue.)
- It’s a quick and easy way to expand your garden through propagation.
When is the Best Time to Divide Perennials?
Fall is a good time to divide perennials as they die back. The soil temperatures are warmer than the air temperatures, which encourages root growth, and that’s a very a good thing.
Rule of thumb: Divide spring-blooming perennials in fall. Divide late-summer and fall perennials in spring.
How to Divide Perennials (Part 1)
Many perennials such as astilbe (like the one pictured) or shasta daisies grow in clumps, and as they get older, the middle of the clump can start to die out. That’s a clear sign it’s time to divide the plant and rejuvenate it.
- First, cut all the dead stems back to where the plant growth is.
- Use snips or deadheaders. They’re perfect for the job of cutting back the dead stems to make dividing easier. Cut back to the plant.
- Dig at the drip line of the plant. (The drip line is the outer edge of a plant’s canopy where water drips onto the ground.) This is where the roots are, and digging here ensures you’re getting the whole root ball. You may sever some roots when you dig and that’s okay. Dig around the plant, and at an angle to get underneath the root ball, lifting the plant as you go.
- Lift the plant out of the hole. Depending on the size of the clump, it can be quite heavy and you may need some help. Roll it onto its side for dividing.
How to Divide Perennials (Part 2)
- Use a shovel or a sharp knife for dividing. A hori-hori knife is a multi-purpose gardening tool and perfect for dividing perennials.
- Make your first cut right down the middle. Often, the roots will guide you as you make your cuts. Cut where the stronger roots are so that that your new clumps will be productive. The center is often woody and unproductive, so discard any plant material that looks like that. Cut the clump (depending on its size and the needs of your garden) into four clumps or more.
- Replant the divisions. Dig holes about a foot deep and wide, and add amendments: 30% amendment to 70% native soil. Then back-fill, water, and continue to water regularly until your plants have gone completely dormant.
For more information on a variety of perennial divisions, check out these sites:
If you have more questions, don’t hesitate to come talk to us here at the garden center!
