Divide perennials and double your pleasure - gardening tips

Sunset, Fall-Winter, 1996

One quick way to double - or even quadruple - the number of perennial plants in your garden at no expense is to divide overgrown and crowded clumping perennials and bulblike plants. Not only do you get new plants to fill the gaps in existing beds or to start an entirely new border, but dividing improves the health of an established plant so it will grow vigorously and bloom profusely.

In mild-winter climates, fall is the best time to divide spring- and early-summer-blooming perennials (in cold-winter climates, divide these plants in early fall so the roots can get established before cold weather sets in). Late-summer- and autumn-blooming plants such as aster, Rudbeckia, and purple cone-flower can be divided in late fall or spring.

WHEN IT'S TIME TO DIVIDE

As clumping or bulblike perennials grow, they put out new growth around the center clump. Some plants - aster and astilbe, for instance - eventually turn woody in the center (this old growth becomes less vigorous or even dies); divide the outer clump into sections, then discard any unproductive growth and save only the healthiest parts of the plants.

Most perennials, however, don't develop a woody clump; you can simply divide the entire plant into sections and replant each section.

To survive, each division must have roots and at least one stem. While you can often divide a plant into dozens of sections, remember that the smaller the section, the longer it will take to establish, mature, and put on a good show of bloom. For best results, divide plants into fewer, larger pieces - unless you're dealing with a very overgrown plant (typical of agapanthus or red-hot poker) or you need a lot of plants to start a new garden.

How often you divide perennials depends on how fast the clumps expand. Some vigorous growers, such as fortnight lily (Dietes) and lamb's ears (Stachys byzantina), often need dividing every two to three years. Slower growers, such as bleeding heart (Dicentra) and peony, need dividing only every five years or so.

If a plant is blooming poorly, has a lot of dead wood in the center, or is cramped and pushing out of the soil, it's time to divide. If the plant appears vigorous and is blooming, then wait.

DIGGING UP PLANTS

The day before dividing a plant, moisten the soil thoroughly so you can dig up the plant more easily. Use a shovel or spading fork to cut a circle into the soil around the plant - 6 to 12 inches beyond the plant's perimeter. Getting large, overgrown plants out of the ground is often the toughest part of the job. With delicate plants, be careful not to damage the roots.

Once the plant is out of the ground, gently tease some soil from the rootball (hose it from fragile roots). Bulbous- or tuberous-rooted plants such as clivia and daylily are easier to divide if you remove all the soil from their roots.

DIVIDING PLANTS

Plants can be divided with a shovel, a spading fork, a knife, a saw, an ax, or pruning shears (clippers), as well as by hand. How you proceed depends on the plant's growth habit, which tools you have, how much time you have, and, most important, the type of roots the plant has.

Plants that have tough, sturdy roots (daylily) usually need to be pried or chopped apart. Fibrous-rooted plants (yarrow) are easy to cut apart with shears or a knife. Brittle or delicate roots (clivia) need gentle handling.

Once the plant is divided, you can cut its foliage back to 4 inches (except on divisions with little foliage). Some gardeners leave foliage of evergreen plants intact, but others say the plants look neater when trimmed.

REPLANTING DIVISIONS

Mix organic matter into the new planting area, and replant the divisions immediately. To allow for settling, plant the divisions about 1/2 inch higher than the level at which they were originally growing. Water well, then keep the soil moist. You can also replant divisions into containers and wait until plants become established before transplanting them into the ground.