Soil and water

Why, when and how to divide perennials


Many gardeners love flowering perennials because you don’t have to plant them every year, saving you labor. However, most perennials require occasional maintenance. A well-maintained perennial will have healthy growth and larger flowers.

Why

Perennial herbaceous plants produce new seedlings each year, which become overcrowded, competing for resources. Over time, herbaceous perennials will often become a dense clump of plant material. The flowers may lose their size and vigor. Often the center of the plant goes out. Dividing perennials will help overcome these problems. Division is also a way to “produce” more plants.

When

Most herbaceous perennials should be divided every three to five years, some more often and some never. Careful observation of the plants will give good indicators of when they should be divided.

As a general rule, fall flowering perennials should be divided in the spring and spring / summer flowering perennials should be divided in the fall. If possible, avoid dividing them when they are in bloom. Immediately after flowering, it is much better than before flowering. Most important is the care they receive during the division. Avoid dividing in hot, windy and sunny weather. Fall division should take place at least six to eight weeks before the ground freezes.

Ron Patterson, EastIdahoNews.com

How? ‘Or’ What

Preperation

Mother plants should be watered a day or two before the operation. To minimize time off the ground, prepare the new location before transplanting. If the roots are to stay out of the soil for more than a few minutes, wrap them in damp paper or wood chips.

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Ron Patterson, EastIdahoNews.com

To treat

Most plants will survive the shock of division if the leaves are cut to about six inches, to reduce the stress of dehydration. The procedure may differ slightly depending on the root system, but in all of them you lift the mother plant by cutting all around the crown, then slide the spade under the root ball to lift it up in one piece.

Spreading root systems such as astilbe, bell, hedge flower, echinacea, or black-eyed Susan roots can often be separated by hand or using a tool into individual plants. Include at least three to five buds with each new clump.

Clumping root systems such as daylilies, rhubarb, red poker, or lily of the valley will often require a shovel or machete to divide the crowns. Each new division should have several eyes, or buds.

Rhizomes (underground stems) such as bearded iris, peony or hosta can be separated with a sharp knife, making sure that there are a few buds at each division.

New plants should be buried as soon as possible with the crown at or slightly above the new soil level. Be sure to tamp the soil around the roots and water well immediately after transplanting. Do not fertilize the first year.

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Ron Patterson, EastIdahoNews.com

Post-division care

Keep the new plant well watered, but not waterlogged, for a few weeks after planting. Thick mulch after the soil freezes will help protect new plants from freezing. Some perennials (oriental poppy, columbine, lupine, monkshood, bugbane) should not be divided. Here is a list of common perennials with information about the University of Minnesota Extension Division.

May your perennials always be beautiful.


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