Your mother probably propagated her favorite flowers in a glass of water on the windowsill. That works fine for some plants, but there are many kinds that require more effort to propagate from cuttings. Some require MUCH more effort.
Of course plants can be propagated from seed, but seeds often produce new plants that are different from the parent. Asexual, or vegetative, propagation always produces new plants that are identical to the parent. One of the easiest ways to propagate vegetatively is with stem cuttings.
We classify cuttings by their maturity. Some plants are best started from young softwood cuttings, while others are easier to start from mature hardwood cuttings, and still others by intermediate semi-ripe cuttings. Consult a reference such as Hortus Third, the American Horticultural Society Encyclopedia of Garden Plants, or the Royal Horticultural Society Dictionary of Gardening for species-specific recommendations. And, don’t be shy about trying more than one type of cutting regardless of the recommendations.
Whether we start with softwood, semi-ripe wood, or hardwood, we want to use clean, healthy cuttings that do not have, and never did have, flowers or flower buds. Take cuttings in the morning and use them as soon as possible, keeping them fresh in a plastic bag so they don’t wilt. Use a sharp knife to carefully scrape a narrow sliver of bark about an inch long from one side near the base. (This wound is often where the first roots develop.) Experts disagree on the necessity of using a commercial rooting hormone, but it can’t hurt. Follow label directions and apply a small dab to the base of your cutting. Use a dibble to make the insertion hole in the starting medium so you don’t rub off the rooting hormone. Water the cuttings with a dilute solution of fungicide. Cuttings from some plants require bottom heat for best results.
Starting a new plant from a softwood cutting is usually your first and best option. Use softwood cuttings for herbaceous perennials and many kinds of trees and shrubs. Softwood cuttings are made from young, fast growing stem tips, taken in the spring, and generally about 3-5” long. Select non-flowering shoots of the current season’s growth. Cut straight across just below a node or make a “heeled” cutting by pulling a young side shoot off last year’s stem, leaving a wedge of old bark (the heel). Remove the lower leaves, and reduce the size of large leaves. Insert the cut end an inch or two into a potting mix consisting of equal parts peat and coarse sand or perlite in a translucent cup.(A translucent cup allows us to see when the roots develop.) Keep the cuttings in an environment that maintains moisture, provides light, and prevents rot.
Softwood cuttings wilt quickly if not kept moist. However, if kept constantly moist, they are not likely to rot. The best way to maintain the cuttings is with an automated system that mists the cuttings for 10 seconds every 10 minutes during daylight hours. This allows them to dry out between mistings, discouraging fungus and mildew attacks. Alternatively, you can pay close attention to your cuttings and mist them with a hand sprayer periodically.
For most of us, a makeshift system that consists of a clear plastic bag tented over the cuttings can be used. Just keep an eye on the cuttings and remove the bag to let them dry out at least once a day. Watch closely for signs of fungus or mildew and spray with a fungicide at least once a week and more often if necessary. When the cuttings have developed roots, often within just a few weeks, they can be potted up in a regular potting mix and cared for as you would any young seedling.
Many evergreen trees and shrubs, including even conifers, can be started from semi-ripe cuttings. Semi-ripe cuttings are taken from the current season’s growth in mid to late summer. These are still soft and pliable at their tips, but hard and woody at their bases. Semi-ripe cuttings are less susceptible to wilting and rot than softwood cuttings, but they take longer to root. Choose 5-7” stems, then cut off the soft tips and remove the leaves on the lower third. Cut off about half of each large leaf. Insert the lower third of the cutting into the potting medium. Water and apply a dilute fungicide. Maintain with mist as for softwood cuttings. Semi-ripe cuttings can take months to root and may need to be overwintered and given a few more months in the next growing season to develop enough roots for safe potting up.
Many broad leaved evergreens, such as hollies, magnolias, and rhododendrons, and some deciduous trees, are best propagated from hardwood cuttings. Hardwood cuttings are the least prone to rotting and wilting, but take the longest to develop roots. Hardwood cuttings are fully mature pieces of stem that are taken at the end of the growing season, in late fall or early winter. Use woody stems from the current season, about 6-8” long, and about the thickness of a pencil. Cut them just above a bud at the top, and just below a bud near their junction with older wood at the bottom. For evergreens, remove the leaves on the lower 2/3 of the cutting and insert it that deep. For deciduous twigs, bury the whole cutting so that the top bud is just below the soil surface. Hardwood cuttings should be overwintered in a cold frame or even in the ground. They will need the next growing season to develop enough roots for safe transplanting.
Don’t be discouraged by all the details! Give cuttings a chance. Remember your mother’s success on that kitchen windowsill! Can’t hurt to try, you never know what results you might see.