Dividing Perennials

Joanne K.,  Pitt County Arboretum E Extension Master Gardener Volunteer

As spring bulbs start to bloom, you will also start to see tips of your perennials poking above ground or showing some new growth. Late winter, early spring is a great time to divide your perennials.

Plant division allows you to maintain the desired plant size, revitalize its growth, and produce more plants for yourself or to share with fellow gardeners.

Division is not needed every year. Many perennials, however, can become too thick after growing for two or three years in the same place resulting in smaller, fewer, or no blooms at all.

Other signs that a plant should be divided include a dead center, sluggish growth, or too large for its space.

1. Aster roots can be easily pulled apart for division.

Perennials can be divided in the fall when the foliage dies back or in the spring when shoots are 2 or 3 inches above ground. Since the plants are not blooming, their energy is directed to establishing roots and encouraging leaf growth before the flowers appear.

If divided in the summer when the plants are actively growing, reestablishing them is much slower. Plants in flower require a lot of energy and dividing them at that time stresses the plant. Also summer heat places a strain on divisions and requires attentive watering, sometimes daily.

Before dividing your perennials, water them thoroughly so it's easier to handle them. Keep the roots moist before planting them in the ground. A bucket with water will replenish the moisture as needed.

With a sharp pointed shovel dig under the roots carefully lifting up the plant. Shake off the excess soil removing any dead leaves, stems, or damaged roots. Be sure to keep part of the growing point (crown) and root system together.

2. Bee Balm, Monarda didyma, is also easy to separate by hand.

3. Daylilies, Hemerocallis spp., with their big clumps need a sharp knife for division.

4. Hosta plants form thick roots requiring a handsaw to separate them.

For some plants the root system can be pulled apart by hand such as Asters and bee balm (Monarda). For bigger clumps such as daylilies (Hemerocallis spp.) and Hostas, you may need to use a sharp knife or handsaw to cut between the crowns maintaining a good section of root. Three to five shoots are recommended for each division.

5. Iris rhizomes can be easily cut apart but be careful not to damage them.

Irises, which grow from rhizomes, will stop flowering when the rhizomes are crowded. A rhizome division needs a few inches of rhizome and one fan of leaves, cut halfway back.

Don't over divide as a small clump will be slow to flower after transplanting.

Immediately plant your divisions in the ground or planter to the same depth as they were. Tamp the soil down to close air pockets and water well.

6. Hellebore plants are best propagated through their seedlings.

7. Columbine should never be divided.

Mature Lenten Roses (Hellebore) are difficult to move. The species spreads easily so digging up and replanting the seedlings will be more successful.

Some plants should never be divided such as butterfly weed (Asclepias), columbines (Aquilegia), and indigo (Baptisia).

More instructions on how and when to divide perennials can be found at:

http://www.clemson.edu/extension/hgic/plants/landscape/flowers/hgic1150.html

More information on the individual plants above can be found at the NC Extension Gardener Plant Toolbox at:
https://plants.ces.ncsu.edu/

Photo credits:
1.    Aster, Joanne K.
2.    Bee Balm, Monarda—Red tubular flowers Dy-e CCBY-SA 3.0
3.    Daylilies, Hemerocallis spp., Joanne K.
4.    Hosta, Joanne K.
5.    Iris, Joanne K.
6.    Lenten Rose, Hellebore, Joanne K.
7.    Columbines, Aquilegia, Joanne K.