Certain varieties of perennials can be used to create new plants. This is accomplished by the use of various propagation methods.
The general methods used include cuttings, division of old clumps, propagation from leaves, and budding.
Some varieties can be propagated by a number of methods; for others, only one way works.
Cutting is the process of removing a small portion of a growing plant and treating it so that roots are developed.
The cutting can then be transplanted and will, in time, produce its own blooms. Cuttings are usually made from a portion of the stem, from leaves, from tubers or from roots.
Cuttings are usually rooted in a mixture of sand and peat moss. Some varieties can be induced to root in water, in sphagnum moss, or in light, sandy soil.
For softwood cuttings, made from the wood stem of soft-stemmed plants, insert small pieces of stem about 2 or 3 inches long in 4-inch-deep (or deeper) flowerpots, with about one-half their length exposed.
Some provision should be made for shading. The flowerpot should be inserted in another pot filled with water, so that there is a steady seepage through the porous clay. The hole at the bottom of the pot should be tightly plugged with a cork.
Practically all perennials can be propagated by cuttings. The clipping itself should be made at a sharp short diagonal, just below a node or joint.
The cutting should be wrapped in damp newspaper and exposed to the air for a half-hour or more. This does not apply to plants which exude a milky juice. Such cuttings should be sprinkled with water and exposed to the air for two hours.
Many perennials can be propagated by causing a leaf to root. Plants with thick fleshy leaves, like begonias and gloxinia, are particularly suited to this method of increasing their number.
The leaf stem is inserted in the rooting medium and cared for as in the case of cuttings. Some plants can be propagated by placing the leaf flat on the rooting medium and weighting it down with pebbles. A slight cut is made through the main vein of the leaf.
The use of plant hormone will materially improve the chances of propagating successfully from leaves, even in the case of plants generally considered difficult to propagate by this method.
Rooting hormones are particularly successful with holly, magnolia, rhododendron, azalea, taxus and many others.
Dividing clumps is one of the simplest methods of propagation. It is, in addition, good for the old divided plants. Many perennials deteriorate if left in clumps for too long a period. Dividing them insures continuous health and growth.
The plants are carefully removed from the soil, in clumps, and divided simply by pulling them apart. Care should be taken to injure the roots as little as possible.
Divided plants are potted, or if the division is done early in spring, as with the hardier perennials, the new clump is planted in another section of the garden. The new planting should be well fertilized and watered.
Layering is another simple method of propagation. It is adaptable only to those plants which root easily when their stems are in contact with the ground. Broad-leaved evergreens in particular (i.e., rhododendron) lend themselves well to this method.
Simple layering involves anchoring the supple stems of plants into the adjacent soil by bending them over and burying them.
Black raspberries, for example, are easily propagated in this way. For plants with less supple stems, a notch is cut about 18 inches from the tip of the stem and propped open with a twig or sliver of wood.
The branch is then bent to the ground, and the notched portion covered with soil. This type of layering is best done in spring or summer. Leaves should be removed from the stem which is being used for propagating.
Serpentine layering is used for plants with long supple stems (vines, for instance) which travel close to the ground.
A number of plants may be obtained from one stem by covering it with earth at different points; the tip should always be left exposed, however.
Air layering is a very modern and popular method, adaptable to trees and woody plants.
A portion of a straight branch or stem is cleared of bark down to the wood, and surrounded with moist sphagnum moss.
The moss should be kept damp. Some manufacturers provide plant food and hormone which can be rubbed into the cut, and a plastic wrap for the moss which is also impregnated with plant food.
After the notch or stripped area has rooted well, the branch is cut off and replanted.