This is a wonderful way not only to increase perennials, but also to keep them young and vigorous. How often you divide them depends on each plant’s individual performance. When growth is so thick it seems to be choking itself, when there’s little healthy new growth and a poor show of bloom, when a clump or crown becomes tough and hard in the center, it’s usually time to refresh the plant by division. Some plants need it almost every other year, some not for many years.
How you divide a plant depends upon how it grows. If there is a central crown of leaves, it can be cut cleanly into two or three sections, each with its own share of roots. Or there may be new, young crowns clustered around its edge that can be pulled or cut off. If the plant simply has a crowded colony of stems and fibrous roots, you can often pull it apart gently into several pieces. Or if it’s the type that sends out rooting runners, you can sever these and replant them. Generally, the old, tired center of the plant is discarded.
In cold climates, even spring-flowering perennials are most safely divided very early in the season, when new growth is beginning. Cool, moist spring weather favors rapid recovery from the operation, and there is plenty of time for the new plants to mature before fall. Summer-flowering and fall-flowering types are also divided in earliest spring. In humid climates the spring-bloomers can be divided in August or early September.
Layering
Almost any perennial with low or low-hanging branches can be propagated by pinning a stem to the soil, several inches from the growing tip. When new growth appears, cut off the rooted stem and transplant it. This propagating method may not produce great numbers of new plants at one time; but it is surely one of the easiest and least troublesome practices—and particularly safe because the new plant is supported by the parent until it is well rooted.
I’ve been intrigued with one good gardener’s method of creating a low hedge from one plant of dwarf lavender. She layered one stem at each side of the original plant. When these two new plants were fairly mature (but not cut away from the old plant), she layered one stem of each. By repeating the process, and locating each new layer in a straight line with the last one, she can extend her hedge as far as she wishes and plant it as she goes, along any lines.
ROCK GARDEN PERENNIALS
Achillea Compositae Yarrow, Hilfoil
Resembling the field yarrow, but dainty, mottled, and tufted. The leaves, some finely cut and ferny, wear thick wool coats. The saucy flowers are in heads, some flat-topped and not unlike daisies.
ageratifolia aizoon (Anthemis aizoon)—Six-inch mat of silver-haired, uncut leaves topped with bright white flowers in May and June.