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Divide and Conquer Perennials Master gardener Maureen Gilmer, host of Weekend Gardening, provides tips on how to divide perennial flowers in the garden.

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Smaller new sprouts of hostas are easily dug and divided when they first appear in spring. (All photos courtesy of Maureen Gilmer) Herbaceous perennials such as these Siberian irises are best dug and divided after they die back at summer's end. A huge old patch of all-green Agapanthus can be divided into dozens of new plants to spread around the garden. Most perennials are best divided in early spring when the bulbs bloom so they have time to become established before the summer heat.

By Maureen Gilmer

May 12, 2008 — Divide and conquer your budget problems. That's the gardener's secret to a cheap or free landscape without purchasing a single new plant. The key is perennials, which are herbaceous plants that do not produce any woody stems or twigs. They sprout anew from the roots in spring and then die back to the ground again at the end of fall. Some of the most well known are daylilies, fluffy astilbe, succulent sedum and aromatic yarrow.

What makes perennials so addictive is that they grow larger each year to cover more ground and bloom prolifically. However, after a few years they begin to decline unless they are divided into many smaller individuals. These new pieces of the mother plant may be replanted in the same area, transplanted elsewhere in the garden or traded with friends to add new varieties to everyone's garden.

It's not uncommon to find huge masses of undivided perennials at older Victorian or early-20th-century homes. Often these colonies do not bloom well because they are overcrowded. They may also have died out in patches to spoil their natural beauty. These old stands are a treasure trove for free, and often rare plant material through division.

Dividing perennials is best done in early spring so new plants can become established before the summer heat. It can also be done in the fall to give them all winter to adapt to the new location. Choose a cool, cloudy day to reduce dehydration of the exposed roots and limit wilting of the foliage. Scheduling the task just before a few days of rainy weather is ideal.

Begin by saturating the ground a day in advance to loosen up the soil within the root zone. Cut the stems and foliage back to just six inches or so to reduce the potential for moisture loss through the foliage. Then dig around the plant to loosen up the root zone and lift it out with a spading fork. Some prefer to use two opposing spading forks to pop the plant out of the ground. If it is too heavy to lift, the clump may be severed into manageable segments while still in the hole.

Wash soil off the roots to reveal how the plant is put together. You'll see whether it spreads by creeping roots known as rhizomes or by offset shoots. Each tells you where natural breaks should be. You may need a sharp knife or long-handled loppers; sometimes even a pruning saw to cut large old clumps, which may have accumulations of dead woody material at the core. Try to sever sections of the plant where it wants to split. That way, you won't cut into vital tissues that could damage its health.

It's always wise to divide a plant so that there are multiple growing points on the new pieces. This allows for any dieback that might occur due to injury or dryness. It's failsafe to allow at least three or more growing points per section.

Strive to divide and replant perennials the same day to limit the amount of time roots are exposed to the open air. Replant as individuals or arrange in small groups where exposure is similar to that of the original mother plant. Enrich the soil for the planting hole with compost. Feed, water and mulch to get the new plants off to a good start. If you have leftovers, be sure to give them to friends.

The easy-to-divide perennials include those above as well as agapanthus, aster, campanula, coreopsis, echinacea, hosta, iris, monarda, gaillardia, canna and phlox. Do not divide asclepias, Oriental poppies, Japanese anemone and columbine. Ditto hellebores.

Imagine if everyone in your neighborhood divided his or her perennials about the same week in spring and fall. All it takes is someone to designate a day, time and location to meet up, and next year your free-trade garden could be the best one ever.

(Maureen Gilmer is a horticulturist and host of Weekend Gardening. E-mail her at mo@moplants.com. For more information, visit: www.moplants.com. Distributed by Scripps Howard News Service.)

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