Plant propagation is the process of multiplying the numbers of a plant, perpetuating a species or maintaining the youthfulness of a plant. There are two type of propagation — asexual and sexual. Asexual propagation involves the vegetative parts of a plant including the roots, stems or leaves. A part of a single parent plant is made to regenerate itself into a new plant, which is genetically identical to the parent plant. There are several advantages to propagating plants asexually. It may be the easiest and fastest way to propagate some species of plants. In addition, it may be the only way to perpetuate some cultivars, and it bypasses the juvenile characteristics of certain species. The Kieffer pear and the Peace rose are two examples of clones that have been asexually propagated for many years.

The major methods of asexual propagation are cuttings, layering, grafting and budding. Cuttings involve rooting a severed piece of the parent plant, while layering involves rooting a part of the parent and then severing it. Budding and grafting involve joining two plant parts from different varieties.

Many types of plants, both woody and herbaceous, are frequently propagated by cuttings (Figure 2.1). A cutting is a vegetative plant part that is severed from the parent plant in order to regenerate itself, thereby forming a whole new plant.

Take cuttings with a sharp knife or razor blade to reduce injury to the parent plant. Dip the cutting tool in rubbing alcohol or a mixture of one part bleach and nine parts water to prevent transmitting diseases from infected plant parts to healthy ones. Remove flowers and flower buds from cuttings to allow the cutting to use its energy and stored carbohydrates for root and shoot formation rather than for fruit and seed production. To hasten rooting, increase the number of roots, or to obtain uniform rooting except on soft fleshy stems, use a rooting hormone that preferably contains a fungicide. Prevent possible contamination of the entire supply of rooting hormone by putting some in a separate container for dipping cuttings.

Insert cuttings into a rooting medium, such as coarse sand, vermiculite, soil, water or a mixture of peat and perlite. It is important to choose the correct rooting medium to get optimum rooting in the shortest time. In general, the rooting medium should be sterile, low in fertility, drain well enough to provide oxygen and retain enough moisture to prevent water stress. Moisten the medium before inserting cuttings and keep it evenly moist while cuttings are rooting and forming new shoots.

Place stem and leaf cuttings in bright but indirect light. Root cuttings can be kept in the dark until new shoots appear.

Stem cuttings. Numerous plant species are propagated by stem cuttings. Some can be taken at any time of the year, but stem cuttings of many woody plants must be taken in the fall or in the dormant season.

Tip cuttings. Detach a 2 to 6 inch piece of stem, including the terminal bud. Make the cut just below a node. Remove lower leaves that would touch or be below the medium. Dip the stem in rooting hormone if desired. Gently tap the end of the cutting to remove excess hormone. Insert the cutting deeply enough into the media to support itself. At least one node must be below the surface.

Medial cuttings. Make the first cut just above a node and the second cut just above a node 2 to 6 inches down the stem. Prepare and insert the cutting as you would a tip cutting. Be sure to position the cutting right side up. Axial buds are always above leaves.

Cane cuttings. Cut cane-like stems into sections containing one or two eyes or nodes. Dust ends with fungicide or activated charcoal. Allow the canes to dry for several hours. Lay horizontally with about half of the cutting below the media surface with the eye facing upward. Cane cuttings are usually potted when roots and new shoots appear, but new shoots from dracaena and croton are often cut off and re-rooted in sand.

Single Eye. The eye refers to the node. This is used for plants with alternate leaves when space or stock material are limited. Cut the stem about ½ inch above and ½ inch below a node. Place the cutting horizontally or vertically in the medium.

Double Eye. This is used for plants with opposite leaves when space or stock material is limited. Cut the stem about ½ inch above and ½ inch below the same node. Insert the cutting vertically in the medium with the node just touching the surface.

Heel cutting. This is an efficient method for stock material with woody stems. Make a shield-shaped cut about halfway through the wood around a leaf and axial bud. Insert the shield horizontally into the medium.

Leaf cuttings. Leaf cuttings are used almost exclusively for a few indoor plants (Figure 2.1). Leaves of most plants will either produce a few roots but no plant, or the roots will just decay.

Whole leaf with petiole. Detach the leaf and ½ to 1½ inches of petiole. Insert the lower end of the petiole into the medium. One or more new plants will form at the base of the petiole. The leaf may be severed from the new plants when they have their own roots, and the petiole can be reused.

Whole leaf without petiole. This is used for plants with sessile or petioleless leaves. Insert the cutting vertically into the medium. A new plant will form from the axillary bud. The leaf may be removed when the new plant has its own roots.

Split vein. Detach a leaf from the stock plant. Slit its veins on the lower leaf surface. Lay the cutting, lower side down, on the medium. New plants will form at each cut. If the leaf tends to curl up, hold it in place by covering the margins with the rooting medium.

Leaf sections. This method is frequently used with snake plant and fibrous rooted begonias. Cut begonia leaves into wedges with at least one vein. Lay leaves flat on the medium. A new plant will grow at the vein. Cut snake plant leaves into 2-inch sections. Consistently make the lower cut slanted and the upper cut straight so you can tell which is the top. Insert the cutting vertically. Roots will form fairly soon, and eventually a new plant will appear at the base of the cutting. These and other succulent cuttings will rot if kept too moist.

Root cuttings. Root cuttings are usually taken from 2- to 3-year-old plants when they have a large carbohydrate supply in their dormant season (Figure 2.1). Root cuttings of some species produce new shoots that form their own root systems, while root cuttings of other plants develop root systems before producing new shoots.

Plants with large roots. First, make a straight top cut; then make a slanted cut 2 to 6 inches below the first cut. Store about 3 weeks in moist sawdust, peat moss or sand at 40°F. Remove from storage. Insert the cutting vertically with the top approximately level with the surface of the rooting medium. This method is often done outdoors.

Plants with small roots. Take 1 to 2 inch sections of roots. Insert the cuttings horizontally about ½ inch below the medium surface. This method is usually done indoors or in a hotbed.

Stems still attached to their parent plants may form roots where they touch a rooting medium. Severed from the parent plant, the rooted stem becomes a new plant. This method of vegetative propagation, called layering, promotes a high success rate because it prevents the water stress and carbohydrate shortage that sometimes plague cuttings (Figure 2.2).

Some plants layer themselves naturally; however, sometimes plant propagators assist the process. Layering is enhanced by girdling the stem where it is bent, by wounding one side of the stem or by bending it very sharply. The rooting medium should always provide aeration and a constant supply of moisture.

Tip layering. Dig a hole 3 to 4 inches deep (Figure 2.2). Insert the shoot tip and cover it with soil. The tip grows downward first, then bends sharply and grows upward. Roots form at the bend and the recurved tip becomes a new plant. Remove the tip layer and plant it in early spring or late fall. This method is successful with purple and black raspberries and trailing blackberries.

Simple layering. Bend the stem to the ground (Figure 2.2). Cover part of it with soil, leaving the last 6 to 12 inches exposed. Bend the tip into a vertical position and stake in place. The sharp bend will often induce rooting, but wounding the lower side of the branch or loosening the bark by twisting the stem may help. This method is successful with rhododendron and honeysuckle.

Compound layering. This method works for plants with flexible stems (Figure 2.2). Bend the stem to the rooting medium as with simple layering, but alternately cover and expose stem sections. Wound the lower side of the stem sections to be covered. This method is successful with heart-leaf philodendron and pothos.

Mound (stool) layering. Cut the plant back to 1 inch above the ground in the dormant season (Figure 2.2). Mound soil over the emerging shoots in spring to enhance their rooting. This method is successful with gooseberries and apple rootstocks.

Air layering. Air layering is used to propagate some indoor plants with thick stems or to rejuvenate them when they become leggy (Figure 2.2). Slit the stem just below a node. Pry the slit open with a toothpick. Surround the wound with wet, unmilled sphagnum moss. Wrap plastic or foil around the sphagnum moss and tie it in place. When roots pervade the moss, cut the plant off below the root ball. Use this method with dumbcane and rubber tree, for example.

The following propagation methods can all be considered types of layering as the new plants form before they are detached from their parent plants.

Stolons and runners (Figure 2.2). A stolon is a horizontal, often fleshy stem that can root and then produce new shoots where it touches the medium. A runner is a slender stem that originates in a leaf axil and grows along the ground or downward from a hanging basket, producing a new plant at its tip. Plants that produce stolons or runners are propagated by severing the new plants from their parent stems. Plantlets at the tips of runners may be rooted while still attached to the parent, or they can be detached and placed in a rooting medium. This method can be used with strawberry and spider plant, for example.

Offsets (Figure 2.2). Plants with a rosetted stem often reproduce by forming new shoots at their base or in leaf axils. Sever the new shoots from the parent plant after they have developed their own root system. Unrooted offsets of some species may be removed and placed in a rooting medium. Some of these must be cut off, while others may be simply lifted off of the parent stem. For example, this method can be used with date palm, haworthia, bromeliads and many cacti.

Separation (Figure 2.2). Separation is a form of propagation by which plants that produce bulbs or corms multiply.

Bulbs (Figure 2.2). New bulbs form beside the originally-planted bulb. Separate these bulb clumps every 3 to 5 years for largest blooms and to increase bulb population. Dig up the clump after the leaves have withered. Gently pull the bulbs apart and replant them immediately so their roots can begin to develop. Small new bulbs may not flower for 2 or 3 years, but large ones should bloom the first year. Use this method with tulip and narcissus, for example.

Corms (Figure 2.2). A large, new corm forms on top of the old corm, and tiny cormels form around the large corm. After the leaves wither, dig up the corms and allow them to dry in indirect light for 2 or 3 weeks. Remove the cormels, then gently separate the new corm from the old corm. Dust all new corms with a fungicide and store in a cool place until planting time. For example, use this method with crocus and gladiolus.

Division (Figure 2.2). Plants with more than one rooted crown may be divided and the crowns planted separately. If the stems are not joined, gently pull the plants apart. If the crowns are united by horizontal stems, cut the stems and roots with a sharp knife to minimize injury. Divisions of some outdoor plants should be dusted with a fungicide before they are replanted. Try this method with snake plant, iris, prayer plant and daylilies.

Grafting and budding are methods of asexual plant propagation that join plant parts so they will grow as one plant (Figure 2.3). These techniques are used to propagate cultivars that will not root well as cuttings or whose own root systems are inadequate. One or more new cultivars can be added to existing fruit and nut trees by grafting or budding.

The portion of the cultivar that is to be propagated is called the scion. It consists of a piece of shoot with dormant buds that produce the stem and branches. The rootstock, or stock, provides the new plant’s root system and sometimes the lower part of the stem. The cambium is a layer of cells located between the wood and bark of a stem from which new bark and wood cells originate.

The following four conditions must be met for grafting to be successful: the scion and rootstock must be compatible; each must be at the proper physiological stage; the cambial layers of the scion and stock must meet; and the graft union must be kept moist until the wound has healed.

Cleft grafting. Cleft grafting is often used to change the cultivar or top growth of a shoot or a young tree, usually a seedling (Figure 2.3). It is especially successful if done in the early spring. Collect scion pieces 3 to 5 inches long that have one or two buds. Cut the limb or small tree trunk to be reworked perpendicular to its length. Make a 2-inch vertical cut through the center of the previous cut, being careful not to tear the bark, and keep this cut wedged apart. Cut the lower end of each scion piece into a wedge. Prepare two scion pieces 3 to 4 inches long and insert the scions at the outer edges of the cut in the stock. Tilt the top of the scion slightly outward and the bottom slightly inward to be sure the cambial layers of the scion and stock touch. Remove the wedge propping the slit open and cover all cut surfaces with grafting wax.

Bark grafting. Unlike most grafting methods, bark grafting can be used on large limbs although these are often infected before the wound can completely heal (Figure 2.3). Collect scion wood 3/8 to 1/2 inches in diameter when the plant is dormant; store the wood wrapped in moist paper in a plastic bag in the refrigerator. Saw off the limb or trunk of the rootstock at a right angle to itself. In the spring when the bark is easy to separate from the wood (known as slipping), make a 1/2 inch diagonal cut on one side of the scion and a 1 1/2 inch diagonal cut on the other side. Leave two buds above the longer cut. Make a cut a little wider than the scion through the bark of the stock and remove the top third of the bark from this cut. Insert the scion with the longer cut against the wood and nail the graft in place with flat-headed wire nails. Cover all wounds with aluminum foil and clear polyethylene plastic.

Whip or tongue grafting. This method is often used for material 1/4 to 1/2 inch in diameter (Figure 2.3). The scion and rootstock are usually the same diameter, but the scion may be narrower than the stock. This strong graft heals quickly and provides excellent cambial contact. Make a single 2 1/2-inch sloping cut at the top of the rootstock and a matching cut on the bottom of the scion. On the cut surface, slice downward into the stock and upward into the scion so the pieces will interlock. Fit the pieces together; then tie and wax the union.

Care of the graft. Very little success in grafting will be obtained unless proper care is maintained for the following year or two. If a binding material, such as strong cord or nursery tape, is used on the graft, this must be cut shortly after growth starts in order to prevent girdling and death of the graft. Rubber budding strips have some advantages over other materials because they expand with growth, do not usually need to be cut as they deteriorate and they break after a short time. It is also an excellent idea to inspect the grafts after a 2 to 3 week period to see if the wax has cracked. If necessary, rewax the exposed areas. After this, the union will probably be strong enough, and no more waxing will be necessary.

Limbs of the old variety that are not chosen for grafting should be cut back at the time of grafting. The total leaf surface of the old variety should be gradually reduced as the new one increases until the new variety has completely taken over at the end of 1 or 2 years. Complete removal of all the limbs of the old variety at the time of grafting increases the shock to the tree and causes excessive suckering. In addition, the scions may grow too fast, making them susceptible to wind damage.