Grafting is botanical fusion. Few aspects of vegetative propagation sound so enigmatic or seem so daunting. But grafts readily occur on woody plants in nature when a branch or limb presses firmly against another.
The branches squeeze tighter as they grow, until the cambium layers of both are exposed at the contact point. If the branches remain in place, the cells will knit together and may merge into a single limb. The horticultural process starts with a section of stem, called a scion, that is surgically attached to a growing plant, called the understock or rootstock.
Professionals graft plants mainly because it is the fastest way to get the largest number of salable-size products from the least amount of tissue of the chosen variety. There are other reasons to graft. The understock may impart some disease resistance or winter hardiness to the scion-topped tree, and control its size as well. Nearly every apple you eat comes from a grafted tree. New rose introductions at the garden center are grafted onto readily available rose rootstock. Most hybrid tea roses are propagated by a technique called “budding,” in which a few dormant buds of one variety are slipped under the bark of a seedling or cutting propagated to be the understock.
Why would a home gardener want to do such a thing? A beloved old tree —injured or threatened by development —could be grafted and perpetuated for future generations. If a tree is damaged at trunk level —by foraging animals, for example —it may be repaired with “bridge grafts.” A frail sport can be grafted onto a vigorous understock. A cascading plant could be grafted onto a straight trunk to produce a weeping tree. Some varieties cannot be propagated by any other means.
The techniques recommended here utilize hardy woody plants during their dormant season and are illustrated with plants for novice grafters to try.
All apples—apple tree varieties, that is—are grafted.
The coloring stems of peach trees and the earliest sign of swelling buds signal the time for grafting fruit trees.
Nearly all perennial fruits are hybrids that can only be propagated asexu-ally. (Consider the seedless orange.) One apple tree grafted with several varieties grows in Gladys Bozenhart’s garden.
Tree peony cultivars are grafted. Roses can be easily shipped and grown from single grafted buds; in a famous example, stems of Rosa ‘Madame A. Meilland’ were sent to the grower Conard-Pyle aboard the last airplane from Paris to the United States as World War II began. Buds were distributed, and on the day Berlin fell to the Allies the superb hybrid tea rose was introduced with a new name: ‘Peace’.
Gladys Bozenhard, an enthusiastic amateur gardener, became intrigued by the idea of grafting when she heard that several apple varieties could be made to grow on one tree. I thought this was a frivolous novelty, but there, on three small apple trees, Gladys had over a dozen varieties. Each tree had four or five kinds growing on separate branches, which ripened through the entire season, from late summer to late fall. When they flower, the varieties can cross-pollinate for heavier fruit set. Sweet dessert types, tart baking kinds, antique varieties, and experimental new ones grow in a 10- by 20-foot area of the garden.
Grafting is one of the most advanced forms of propagation, but it is not out of the reach of the amateur. Learning to graft is a bit like learning to drive a car —it must be witnessed firsthand and practiced under the eyes of a teacher. But once learned, grafting skills are never forgotten.
Gladys enrolled in a short course in grafting and discovered she had the knack. She would be surprised to hear that a 50 percent success rate is desirable, since her plants nearly always prosper.
The most startling revelation from these amateur grafters like Gladys, however, is that they contradicted the accepted practice of grafting when trees and shrubs are completely dormant —in midwinter. Most of these gardeners undertake their projects in late winter to early spring —just before flower buds swell on the plants they are using. These people seemed intuitively to realize that in a few weeks, the plants would begin their most active growth of the year, when they are most determined to persevere.
Among Gladys Bozenhard’s essential equipment is a clipboard for recording dates of procedures, variety of scion, and understock.
Rudimentary apical wedge grafting calls for inserting a V-shaped scion into a corresponding cut in an understock of the same diameter.
The inverted saddle graft involves blunting the cut point of the understock and rounding the wedge cut of the scion. The cambium must line up exactly.
The key to successful grafting is bringing the cambium layer from one plant into perfect contact with the cambium layer of another. The parts must be compatible —for example, from two species in the same genus. Stem sections must retain polarity —up stays up.
Many of the same tools used for stem cuttings can be adapted to grafting—pruning shears, alcohol for sterilizing, rubber bands, and paper towels. A few others may be called for, such as wax to seal the top of the scion. A sharp knife is indispensable, and professional grafters have special knives for each procedure. For beginners, a snap-blade utility knife is fine, and heavy leather gloves should be worn for protection. A pencil and a notebook are necessary for keeping careful records on the plant sources and the dates of the procedures.
To facilitate joining scion and understock, different kinds of cuts have been developed for various plants and stages of growth. The cuts expose the greatest amount of tissue whenever possible and often provide physical stability.
Two equal-size twigs could be cut straight across to expose the cambium, but it would be difficult to join these pieces. The grafters’ version of this rudimentary cut is a diagonal slice on the top of the understock and on to the bottom of the scion. More area is provided for stability, and more cambium is exposed. When these elements are spliced and bound, a “whip graft” is formed.
In a “saddle graft,” the scion is cut into a V shape, and the understock is cut into a corresponding shape. The scion, which will become the leader, is lowered onto the understock, which will become the trunk and roots.
A “wedge graft” is similarly straightforward. The scion is cut into a pointed wedge. The understock is cut straight across, and then a perpendicular slit is made. The pointed scion is inserted in the slit and the two pieces are banded together. In a “cleft graft,” an understock of a greater diameter than the scion is sawed straight across, and then V-shaped notches are cut into it through the sawed top. The scion or multiple scions are cut to precisely fit into the slotted openings of the understock so that the edges of their left or right side—where their cambium is exposed —come in exact contact with the cambium layer of the understock. Melted grafting wax is painted over the cut areas to seal them and hold the parts in place.
In “side veneer grafts,” often used for evergreens and Japanese maples, a long, shallow cut is made in the bark of the understock, and a smaller scion is fashioned with an opposing cut.
In “approach grafting,” two plants growing in pots are placed side by side. One gets a V-shaped groove and the other is carved with a corresponding ridge. The two plants, still in their pots, are then bound.
“T-budding” is demonstrated here. “Rind grafting” is similar. A T-shaped slit is made on the bark of the understock. The bark is loosened with the back of the blade. The bottom of the scion is trimmed like a reed and slipped beneath the bark. Like all grafts, the cuts must be kept moist and sealed. After the scion sprouts, the top of the stock is cut away.
Experienced gardeners graft herbaceous plants, and in the laboratory, micrografts are performed on just-sprouted seeds. By now, you are probably recalling that most grafting operations have to be demonstrated, witnessed, and then practiced. But every grafter begins by taking his or her first cut.
Magnolia ‘Elizabeth’ was bred at the Brooklyn Botanic Garden from M. acumenata and M. denudata. The chance seedling would be difficult to duplicate but easy to reproduce via grafting.
A demonstration of rubber band tying.
Cleft grafting is recorded in the propagator’s sketchbook: wedge-cut scions are inserted, cambium to cambium, into a vertical cut in a sawed stem, and held in place with grafting wax.
With thin-barked Japanese maples, a variation of a T-bud and a splice graft is made by inserting a twig with a diagonal sliver cut from the side opposite a bud into a T-shaped incision through the bark.
The graft is carefully positioned
and secured with a rubber band.
T-budding is a method most often used for ornamental woody plants—especially roses (demonstrated here). Begin by cutting a scion stick, snap off the thorns, and with the bud facing upward make a shallow cut that goes in, passes behind the bud, and comes out again (1). Then peel the wood from behind the bud and bark and discard it. The understock gets a T-shaped cut and the bark is slipped free using the back of the knife blade (2). The bud is eased beneath the flaps of bark (3) and cut flush at the top into a shield shape that fits snugly. The cut and bud are entirely covered by a tied rubber band (4), which will disintegrate by the time the accepted bud begins growth—the following spring if the graft is made in summer. The graft can also be covered with wax (5). Prior to the mass popularization of hybrid tea roses, cultivars such as ‘Marie Louise’ (1813) (6) were grown from greenwood cuttings, but demand and the fact that many tea roses have feeble root systems made T-budding ubiquitous—until recently. Concerns about hardiness and disease are bringing back the demand for “own-root” roses.
Gladys Bozenhart’s early grafting efforts were made in the field —with her own apple trees. Her technique was performed in midspring with dormant twigs of one variety, grafted onto branches of established trees. From her start as a curious gardener, she has gone on to guide a volunteer effort to build the antique-apple collection at Tower Hill Botanic Garden in Boylston, Massachusetts. Now she is helping Sturbridge Village Historical Gardens create a collection starting with trees that are bench grafted—the indoor version that uses nursery-supplied rooted dormant understock, and is demonstrated below.
Gladys uses pruning shears, a sharp knife, alcohol for sterilizing the knife between cuts (1), rubber bands, paper towels, and a dab of wax to seal the top of the scion after each graft. She uses the version of the splice or whip graft called a “whip and tongue.” First, Gladys holds the scion and understock side by side to determine the exact point where they are the same thickness (2). The pieces are trimmed 2 inches above the spot on the understock and 2 inches below the spot on the scion (3, 4). The first cut for grafting is a diagonal slice 1½ inches long made to the bottom of the scion (5). This is followed by a diagonal cut of the same size at the top of the understock (6). Gladys checks to see that the cuts match (7), and she retrims only if absolutely necessary, because whittling might distort the sliced sections. A second cut is made into each piece, a third of the way down the scion and a third of the way up the understock (8, 9). The cut should go straight into the stem and penetrate about ¾ inch. The scion and the understock should fit so well that they will hold themselves together once joined (10). The grafted area is secured firmly and kept from drying out using a rubber band to completely cover the area of the joined material (11). The roots of the labeled graft are kept moist in a plastic bag (12) until potting, which should happen soon. The potted plant can be summered in a protected spot outdoors and then planted in a nursery bed or its ultimate spot in the garden.
After connecting cambium to cambium, the key to a successful graft is to keep the plants firmly attached and full of moisture while the cut areas are fusing. Grafting was once popular, but the cut rubber band has become the preferred method. In Great Britain, patches of pure crepe rubber are used to cover smaller grafts, such as those involving buds. The rubber disintegrates before it can squeeze the growing wood, and the covered buds can grow right through the brittle rubber. Some grafters tape a bit of plastic film over the banded area of the graft for a week or two to retain moisture.
Professional growers pot up their grafted plants and place them in shaded greenhouses or plastic-film-covered Quonset-hut-like hoop houses with temperature and humidity controls. In early autumn, the plants can be placed back into the greenhouse, planted in a nursery bed, or wintered over in a cool place such as a mud-room or unheated garage.
Most home propagators, however, improvise to provide a suitable environment for the new grafts —Dick Figlar keeps his newly grafted magnolia trees inside by a sliding glass door for a few weeks until they can go outside to a sheltered spot, while Gladys Bozenhard pots her grafted bare-root saplings in gallon nursery pots and sets them on a chair next to the kitchen table to keep an eye on her projects for a couple of days. She then moves the saplings to the screened porch for a short time before setting the pots in a sheltered garden spot.
The newly grafted plants in pots will sprout leaves and soon heal their joined sections. The dormant may not grow until the following year. Then, the scion should be encouraged to become the only top growth of the plant. If a bud graft was made for a tree variety, any growth from the original understock should be cut off just above the graft so that the bud can grow and become the new leader. Any buds that develop below the graft on the understock should be rubbed off so that the former variety will not overtake the new plant.
You may be intimidated or stimulated by these procedures. Either way, attempt a simple graft. One thing is certain: Rare is the gardener who successfully grafts a plant just once.
To graft magnolias, Dick Figlar uses the chip-bud method in mid-spring, a week before buds swell. His favorite tool is an injector razor blade. He inserts the blade above the bud and cuts beneath and toward it (1). A second angled cut is made below the bud continuing away from it (2). The crosscut frees the chip and bud (3). The chip bud will be inserted into a corresponding cut made to the understock.
The chip bud graft is wrapped with a rubber band (1). Then Dick covers it with clear plastic to keep the humidity high for about a week (2). The cells fuse and the graft takes. The graft is well established the following spring (3). The top of the understock seedling will be cut off, and the scion shoot will become the new leader.
