Propagating plants from cuttings allows you to increase your supply of a special perennial, shrub, or tree already in your garden, or to start plants from a friend's garden. Unlike most plants raised from seed, those grown from cuttings are identical to the parent plant. Cuttings taken from the stems of plants are of three types, depending on the maturity of the parent plant: softwood, semihardwood, and hardwood. Some kinds of plants can also be started from leaf or root cuttings.
Some plants will root successfully from a leaf or a portion of one; examples include rex begonia, African violet (Saintpaulia), and mother-in-law's tongue (Sansevieria). Follow the techniques described below.
Rex begonias are propagated by making cuts in the large veins on the underside of mature leaves. Lay the leaf flat, cut side down, on the rooting medium; then enclose the container in a plastic bag. In time, new plants will grow at the point where each vein was cut.
To root leaf cuttings of African violets, insert a young leaf with an inch or two of stem into a rooting medium made of 1 part peat moss and 1 part vermiculite, perlite, or coarse builder's sand. Enclose the container in a plastic bag to retain humidity. New plants form at the base of the stem.
To root leaf cuttings of mother-in-law's tongue, cut a leaf into 3- to 4-inch-long sections. Insert these pieces into the rooting medium, covering as much as three-fourths of their length. A new plant will eventually form at the base of each piece.
Related: Propagate succulents
SOFTWOOD AND SEMIHARDWOOD STEM CUTTINGS
Taken during the active growing season from spring until late summer, softwood cuttings are the easiest stem cuttings to take and the fastest to root. They come from relatively soft, flexible new growth. Many perennials, shrubs, and trees can be propagated by softwood cuttings, including coleus, forsythia, crape myrtle (Lagerstroemia), geranium (Pelargonium), penstemon, mock orange (Philadelphus), plum, pomegranate, rose, and weigela (to name just a few). Semihardwood cuttings are taken somewhat later in the growing season, usually in summer or early autumn. A semihardwood stem is firm enough to snap if bent sharply; if it just bends, it's too mature for satisfactory rooting. Among the plants that can be propagated from semihardwood cuttings are boxwood (Buxus), camellia, citrus, escallonia, euonymus, holly (Ilex), olive, and rhododendron.
The procedure for rooting these two types of stem cuttings is the same.
You make hardwood cuttings in autumn or early winter, when plants are dormant. Many deciduous shrubs and trees can be propagated by this method, including most of those mentioned above under softwood and semihardwood cuttings; other candidates include currant, fig, gooseberry, grape, privet (Ligustrum), mulberry (Morus), quince, and spiraea.
Any plant that produces sprouts from its roots will grow from root cuttings. Some examples are bear's breech (Acanthus), Japanese anemone, blackberry, trumpet vine (Campsis), globe thistle (Echinops), Oriental poppy (Papaver), and raspberry.
Make root cuttings when the plant is dormant ― in late fall or early winter, for most species. You can dig up an entire plant or just a section of its roots. With a sharp knife, remove vigorous, healthy pieces of root 2 to 4 inches long; those growing close to the crown will form new plants most quickly. (Note that rooting hormone is not needed, and in fact may actually delay rooting.) If you only have a few root cuttings, you can place them upright in a container filled with damp potting mix, with the top cut ends (the ends that were closest to the crown on the parent plant) just at soil level. For larger numbers of cuttings, fill a flat to within an inch of the top with potting mix; lay the cuttings flat on top of the mix, then cover them with 1/2 inch more mix.
Water the planted containers well. Then place them in a growing area such as a greenhouse or cold frame and provide protection from direct sun. Once stems and green leaves have formed, move the containers into full light and water them as needed. When the young shoots are several inches tall and new roots have formed (check by gently digging up a cutting), transplant them to individual pots and feed with liquid fertilizer.