The best time to divide your perennials is in the spring. There are several reasons why you may want or need to divide your plants- some plants spread very quickly and may take over your garden if they are not divided; some can be divided to increase the number of plants you have or be given to others; and some plants should be divided to promote new flower growth and maintain plant health. Although this task may seem intimidating or daunting, once you have mastered the technique, you will enjoy your perennials for even more years to come!
Be sure to water well 1-2 days before dividing. Cut foliage back to 6” or half the plant to make it easier to divide. Cutting back the plant will also mean that the plant has less foliage to support while it is adjusting to the stress of being divided. It is also a good idea to have the place where the divisions will go already prepared. Having new holes dug will decrease the amount of time the plant stays out of the ground.
You will need a shovel or a spade to first dig up the plant. Take the shovel or spade and cut directly down into the soil. This should be done a few inches away from the outer edge of the plant so the root ball is not damaged. Once you have done this all around the plant you will be able to lift the plant out. Do this by hand or by using the shovel as a lever. Just be sure to keep as much of the soil attached to the root ball as possible. Once the whole plant has been removed you will have to decide if one or more divisions will be necessary. The best way to divide the plants is to just use the spade you used to dig it up. You may hear some ripping as the roots separate, but the plant should be able to recover from that slight stress. Plant divided plants as quickly as possible to avoid the root system drying out from wind and sun exposure.
After dividing, make sure your plants are adequately watered. Check the soil around the plants every few days to see if watering is necessary.
Planting & Transplanting Iris
Irises love the heat and the drier weather of summer and late summer dividing will reduce the incidence of bacterial soft rot. Most Iris need to be divided every three to five years. If your plants are not producing many flowers, you know it’s time to divide. After removing from the ground, use a sharp knife to separate the rhizomes. Dip the knife in a ten percent bleach water mixture after each cut to sterilize and prevent disease from spreading. While dividing, make sure to inspect the rhizomes for iris borer and soft rot. When dividing, the Iris borer will be a mature pink caterpillar inside the rhizome and it will be mushy to the touch. Bacterial soft rot often accompanies iris borer damage. If there is evidence of Iris borer, spray with insecticide the following spring. To avoid any decay on the new breaks or cuts, dust the rhizomes with a powdered fungicide. See our garden store for advice on what products to use. Remove and discard the old rhizomes and replant the younger smaller rhizomes that grow off the older stems. The new transplants should have a firm rhizome with roots and a fan of leaves. Replant in a sunny, well-drained garden spot. Dig the hole about 5 inches deep and build a small mound in the middle to place the rhizome. Place the rhizome on the mound allowing the roots to fall down either side and cover the roots so that the rhizome is ever so slightly exposed. Do not plant rhizomes too deep or it may rot or not flower. Fall sanitation is very important in the control of Iris borer. After the first hard frost remove and destroy the old iris foliage and plant debris to remove any eggs. Keep well watered, but not too wet.
Here is a list of some other perennials that can be divided in spring to summer:
- Achillea, common name Yarrow
- Anaphalis, common name Pearly Everlasting
- Baptisia, common name Wild Blue Indigo
- Campanula, common name Bellflower
- Centaura, common name Bachelor’s Buttons
- Coreopsis, common name Coreopsis
- Corydalis, common name Corydalis
- Dianthus, common name Dianthus
- Dicentra, common name Bleeding Heart
- Echinacea, common name Coneflower
- Euphorbia, common name Euphorbia
- Helianthus, common name Perennial Sunflower
- Hemerocallis, common name Daylily
- Heuchera, common name Coral Bells
- Hosta, common name Hosta
- Hosta, common name Hosta
- Iris, common name Iris
- Lamium, common name Dead Nettle
- Liatrus, common name Blazing Star
- Lysimachia, common name Lysmachia
- Monarda, common name Beebalm
- Papaver, common name Poppy
- Peony, common name Peony
- Rudbeckia, common name Black Eyed Susan
- Salvia, common name Salvia
- Sedum, common name Sedum
- Veronica, common name Veronica