Few of us enjoy wall-to-wall people, so it’s easy to feel empathy for overgrown garden perennials as summer ends. During the spring and summer months, healthy flower and foliage clumps expand, growing taller and wider. By fall, your garden may be short on the elbow room that plants need to grow and flower in spring.
September is the perfect time to deal with this overcrowding. While dead or diseased plants may need to be removed and tossed, your favorite perennial plants can be divided into several smaller plants, leaving ample room for new growth in springtime.
Divide and Conquer
If a garden plant has grown too tall, it can be pruned down to size with shears like these on Amazon. But if the root structure has increased and is taking up too much space in the garden bed, you need to divide the clump into pieces. This process is known as division. Since it creates new plants, it is often discussed as a form of plant propagation.
The process of division looks a lot like transplanting, except that you cut apart the clump before replanting. It's not a complex procedure:
- Dig up the plant, roots and all using a shovel like this one at Home Depot
- Separate the rootball clump into two or more pieces - you may need a sharp implement like this hori hori knife from Amazon
- Replant one of them in the original space. The others can be replanted around the garden or given away to neighbors.
Since division stresses a plant, it’s best to avoid adding heat stress to the package. Act when the weather is cool but not cold. Fall is often a good season for garden work and many perennials divide best in fall. Act some four weeks before the first hard frost so that the plant’s roots have time to establish before winter.
8 Popular Garden Plants to Divide in Fall
Most perennials are best divided in fall, just after they finish flowering. Here are eight plants that make that list.
1. Asters
When you're growing asters, divide them every three or four years to keep those flowers coming. When you're splitting the clumps, toss out the oldest rhizomes, only keeping young, healthy sections. Replant them shallowly so that the rhizomes stay a little above the soil.
2. Coral Bells
Fall is the best time to divide coral bells if they're overcrowded. Dig up a clump and divide it into two to four sections. Replant each in prepared planting sites.
3. Cranesbill (Hardy Geraniums)
If you're growing cranesbill in your backyard, you know that these tough and beautiful perennials grow in clumps. They bloom all season long and can become overgrown in a few years. The best time to divide them is when they are done flowering in fall.
4. Daylilies
The lovely daylily flowers only live for one day, so it’s sad when – over time – the blooms get smaller and smaller. Dividing daylilies in fall works well to rejuvenate them. Dig up the clumps then divide them, leaving three fans of leaves and ample roots in each division.
5. Hostas
These shade favorites grow fast. Healthily growing hostas can double their size in a few good seasons and will develop dead centers in their crowns that come to look unattractive. That makes them good candidates for fall division every three or four years. Toss out the dead areas.
6. Iris
You can keep an iris growing well for a few years, then inevitably the plants seem to get choked out. Dividing them in fall means better blooms in spring.
7. Peonies
Peonies happen to be my personal favorites, so I never feel I have too many. But as the peony blooms spread beyond their allotted bed, it’s time to divide them and fall’s the best time. Dig up a root clump of roots and carefully clip it loose from the parent plant. Cut it into sections, leaving at least three buds in each division, then replant.
8. Salvia
It’s hard to find a more reliable flowering perennial than salvia, a plant known for its feathery foliage and gorgeous spikes of blooms that attract pollinators. They grow fast and spread, so plan to divide them every few years.
Top Tips for Dividing Perennials
- Wait for cooler weather.
- Water the soil thoroughly the day before dividing perennials.
- Dig up the entire rootball.
- With a sharp spade or shovel.
- When you are dividing, give each section roots and shoots.
- Replant asap to the same depth.
- Water well after transplant and keep the soil moist until the first freeze.
