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Many perennials require dividing to prosper

If you grow only perennials, and many people do, you perhaps think you have nothing to do but watch for them to emerge in the spring, water and perhaps fertilize.

If you grow only perennials, and many people do, you perhaps think you have nothing to do but watch for them to emerge in the spring, water and perhaps fertilize.

If you are an experienced perennial grower, you will know there is a bit more to it. One task is to divide them when they get overcrowded or stop blooming as well as they used to.

And early spring is the best time to do it.

What perennials really need is to be divided as soon as the frost is out of the ground and the soil has dried out.

Here is a list of those to divide now, keeping in mind that they need to be divided every one to three years: Aster, penstemon, monarda, dianthus, coralbells, cornflower, delphinium, foamflower, fernleaf bleeding heart, chrysanthemums, physostegia, painted daisy, shasta daisy, spiderwort, tall phlox, coreopsis and yarrow.


Perennials that need to be divided every three to five years and can be divided now are: astilbe, campanula, gaillardia, rudbeckia, daylily, liatris, Jacob's ladder, mallow and veronica.

Those that need to be divided only infrequently, like every five to 10 years, may be divided in early spring, too: perennial geranium, aruncus, hosta, alchemilla, pulmonaria, meadow rue, filipendula, heliopsis and Siberian iris.

Wait until late summer or early fall for these: Asiatic lily, bearded iris and peony, if needed. Peonies need not be divided unless they are blooming poorly. The trouble may be that they are planted too deeply. Peonies should not be deeper than 2 inches from the surface, or in too shady a spot.

The following should not be divided: baby's breath, balloon flower (platycodon), cimicufuga, butterfly weed, clematis, evening primrose, baptisia, flax, lupine, monkshood and Russian sage.

Divide these only if you need to propagate them: cimicifuga, trollius and yucca.

To divide, cut or pull them apart. First dig up the entire clump.

You will note that the center root system is hard and woody and the roots along the outside have small energetic roots growing from them.

If the plant is old, you may have to get them apart by placing two spading forks back to back. Throw away the woody centers and use the younger roots growing at the edges for the new plant or plants. Each division should have two or three new shoots and a good segment of healthy roots. The new divisions also should have strong roots to go with those tops.


The new plants should grow well and bloom at the proper time. The divisions have an entire summer to recover the stress of dividing and grow healthy plants. You will be glad you undertook the tough task of dividing them.

Collins is The Forum's garden columnist. Write to her by mail at The Forum, Box 2020, Fargo ND 58107, or direct e-mail to her at dorothycollins@i29.net

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