PROPAGATING MINIATURE PERENNIALS
One item in our Connecticut landscape that’s completely out of scale with its surroundings is the monstrous cold frame near the back boundary line. The cement-block wall goes down below the frost line, and up high enough to make room for winter storage of fairly good-sized plants. The discarded storm windows are hinged across the back and completely removable in summer, when they are replaced by light wooden frames of the same size with laths nailed a lath-width apart. The construction slants toward the south, to make the most of all winter sunshine; light shading is necessary in summer to protect tender seedlings and rooting cuttings.
The cold frame serves dozens of purposes and has more than paid for itself with plants it has protected or produced. When we plant perennial seeds in the cold frame, we throw a piece of burlap across the top and keep it moist until they germinate. Tender seedlings spend their first winter within its walls, and so do newly rooted cuttings. Questionably hardy perennials or any that we acquire in fall are held over until spring. Every year, it seems as if we take more out of the cold frame than we put into it!
Other, smaller, portable devices are equally useful for all kinds of summer propagating. Low square or rectangular wooden frames can be set over an area of prepared soil and the top covered with glass or polyethylene to keep the soil from drying out. An empty fruit crate from the grocer can be equipped with a glass or plastic top. A few cuttings can be rooted in soil in some shady spot with a clear glass jar inverted over them. There are many devices that keep soil moist and air humid while seeds germinate or cuttings root. How large or elaborate yours should be depends on how much propagating you want to do.
Seeds
Many hard-to-find miniature perennials can be easily grown from a twenty-cent packet of seed. You can also harvest seeds from your own plants; but only natural species will “come true.” Complicated hybrids will have unpredictable offspring, most of them not particularly desirable.
We plant seeds of most biennials and perennials in June, when the soil is comfortably warm and the seedlings will have the whole summer to grow large and lusty. Some of our own seeds that ripen in midsummer are planted as soon as we can harvest them; those that mature later are usually stored on a cool shelf in the cellar in plastic boxes or little pill bottles that keep them dry.
Soil for the seed bed is sifted to remove pebbles and debris, and mixed with equal quantities of sharp sand and peat or sieved leaf mold. To prevent “damp-off,” a fungus that chokes off stems at the soil line, soil should be sterilized if at all possible. Small quantities may be baked in the oven. Special easy-to-use fungicides are also available; follow label directions.
Rocks, water, and planting—an effective combination of all the elements of a rock garden. (Mr. and Mrs. Norman Cherry)
Most seeds are covered to the depth of their diameter; very fine seeds are merely firmed down into the soil. Seeds with hard coats may be gently nicked with a knife or soaked in water for a day or so. Some seeds, like primroses, need to be treated as if they had wintered outdoors before they will germinate. You can put them in moist sand in a small, tight container and alternate freezing in the ice compartment and thawing in the warmer part of the refrigerator for several days. Or you can plant these seeds in a small box or flat of their own and leave them outdoors, in a protected spot, where winter will supply its own natural conditions.
Cold frame planted and ready for top made from discarded storm windows
Some seeds germinate faster in the dark, some with light; some like cooler temperatures than others; some come up in seven days, some take months or even a year. Seed packets usually supply pertinent information.
Seeds will not germinate in dry soil, or if allowed to dry out even temporarily during the critical period. To avoid washing out fine seeds, water gently with a fine mist, or set the flat or other container in water up to the level of the soil inside. When the soil surface looks shiny and moist, remove the container and set it aside to drain.
When the first “true” leaves are of fair size, transplant the seedlings to peat pots, or flats, or rows in a prepared bed or cold frame. Shade against sun and wind until they resume growth.
Stem Cuttings
Many perennials can be propagated easily and in quantity by rooting softwood cuttings like those of trees and shrubs. Tip cuttings three or four inches long are usually best, with all the flower buds and the lower leaves removed. Some types, such as dianthus and lavender, root faster and more surely if the cutting is taken with a heel.
For spring-flowering varieties, take stem cuttings after flowering has finished and up until midsummer; for those that bloom later, take cuttings in May or June.
Division
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.