Sooner or later, most perennials need to be divided. Perennial plants typically increase in size by producing shoots and roots on the perimeter of the plant. After 3 or 4 years, the clump may die out in the center, overrun its space, or produce fewer flowers. When these things happen, it’s time to divide.
The dividing process is fairly simple. You will need a few tools, which may include a shovel, garden fork, knife, scissors, and rubbing alcohol. If your soil is dry, water the bed a few days in advance. Have a new planting site in mind and prepared before you begin to make the process go both quickly and smoothly.
Steps to Take
Remove any dead foliage from the plant, then dig around the plant so that it can be lifted in a clump. Next, split the plant with a fork, inserting it deep into the clump. If the roots are tightly compacted or very woody and won’t break apart, you can divide them with a sharp knife. This may be damaging to the roots so cut them as little as possible. Once divided, the clumps are ready for replanting. Water and care for them as you would any newly planted perennial.
Perennials with rhizomes, such as iris, can be lifted after flowering. Cut the rhizomes into sections. Each section should have one fan of leaves. Replant the sections placing the rhizomes just barely below the surface of the soil.
- Spring and summer flowering perennials are best divided in the fall.
- Late summer and fall blooming perennials are best divided in the spring.
- Try to avoid dividing perennials on very hot days. The heat of the sun can be stressful to the plants.
- Use clean equipment. Disinfect knives or scissors with rubbing alcohol to avoid spreading disease.
- Don’t be afraid to “dig in” and divide your perennials. They are tougher than you think and the benefits of dividing are worth the effort!
Perennials to Divide in Early Spring or Fall
Campanula, Centaurea, Lamium, Astilbe, Eupatorium, Trollius, Alchemilla, Pulmonaria, Salvia, Sedum, Brunnera, Stokesia, Coreopsis, Chelone, Veronica, Achillea, Hemerocallis, Hosta
Perennials to Divide in Spring, Preferably April
Asters, Chrysanthamums, Rudbeckia, Boltonia, Monarda, Echinacea, Helenium, Gailardia, Grasses, Helebores, Stachys, Sedum, Plumbago, Tricyrtis, summer blooming Alliums
Perennials to Divide in Late Summer or Fall
Amsonia, Daylily, Geranium, Hosta, Iris, Peony, Fillipendula, Cimicifuga
Perennials to Divide When Dormant or After Bloom
Dicentra, Allium, Primula, Dodecathion, Tradescantia, Mertensia
Perennials That Are Difficult to Divide
Because of the ways certain plants root themselves, we recommend not dividing perennials such as Baptisia, Dictamnus, Echinops, Dianthus, Poppy, and Milkweed.
Planting Divided Plants
Once divided, the clumps are ready for replanting. Water and care for them as you would any newly planted perennial. Add Biotone and amendments, then mix into the planting area or bed. Dig a planting hole and spread the roots out. Break up any large clumps of soil before lightly pressing the soil down around the plant.
If your perennial is in bud or bloom when you plant it, consider cutting these and enjoying them in a vase. This allows the plant to focus energy on growing roots. Water thoroughly after planting.