Contact: Diane Relf, Extension Specialist, Environmental Horticulture
Posted April 1997
One of the joys of a perennial garden is watching the plants grow and fill out the spaces allotted to them. However, herbaceous perennials can outgrow their alloted space so they need to be divided periodically, discarding the older center growth and replanting only the strong growth from the outer edge of the clump. This 'invigorates' the plants with the additional benefit of creating more plants for yourself and to share.
To divide a plant with a root mass such as yarrow or shasta daisies, insert two spading forks back to back into the clump and bring the fork handles together, prying the clumps apart. Don't be afraid of breaking the roots. This is a necessary evil in the process of breaking up the clump. As long as you have root and stems on each piece you can break up a clump into as many pieces as you want.
A rhizome, unlike a root, is an underground stem. It bears roots but also has prominent leaf buds or eyes. Many perennials produce rhizomes: Achimenes, Helleborus, and Hosta. Dig up the rhizome and, using a clean sharp knife, cut off pieces which bear one or two eyes. Dust the cut ends with a fungicide or a rooting powder containing a fungicide to prevent rot or disease before replanting the pieces.
Divide fall-flowering plants in the spring, and spring and summer flowering plants in the fall. The frequency of division depends on the plant itself. For example, Monarda and Oenothera should be divided every two or three years. Phlox, Astilbe, Hemerocallis, and Physostegia should be divided only every three or four years.
Stem cuttings are frequently used for propagating the low growing shrubby perennials such as Phlox and Penstemon as well as the foliage perennials like Sedum and Veronica. Cuttings should be made in mid-summer from spring blooming plants like Phlox and in late spring from summer and autumn flowering plants like Sedum. Take cuttings of 2 to 3 inches in length in early or mid-morning. Dip these in a root-promoting hormone and plant into rooting medium. The cuttings may be kept out-of-doors in a shady, protected spot where they can be kept moist. After top growth extends several inches, the plants can be set into permanent garden locations.
You can also propagate certain plants by bending a branch down and covering with soil. The part of the stem which is buried will produce new roots. Hardy periwinkle, St.-John's-Wort, and several other creeping perennials will propagate this way.
It is an enjoyable, intriguing and gratifying experience to propagate perennials on your own. It requires no elaborate or expensive equipment, just time and patience on your part.
(Prepared by Jennifer Shuster, Extension Technician, Consumer Horticulture, Virginia Tech, Blacksburg, VA 24061-0327.)
Visit Virginia Cooperative Extension test