Grafting is the joining together of two living plant parts so that the whole grows as one plant. The rootstock provides the roots and a short length of trunk. The scion becomes the rest of the trunk, plus the stems, leaves, flowers, and fruits of the grafted plant. The graft union never moves; all growth above this union retains the identity of the scion, and all growth below the union retains the identity of the rootstock.
Grafting is useful for multiplying clones (genetically identical plants), whether the clone is a ‘McIntosh’ apple, a ‘Sargent’ cherry, or some nameless apple tree bearing tasty fruits. An old, dying apple tree can be perpetuated by grafting one of its stems onto a young rootstock.
Why Graft Trees?
Grafting is a way to multiply plants that don’t form roots readily as cuttings or come true from seeds.
The rootstock itself can also serve other useful purposes. It may influence the form of a plant. Weeping cherry growing on its own roots merely creeps along the ground; grafting it high on an upright trunk of a non-weeping cherry rootstock will bring the weeping head high off the ground. A rootstock might influence the eventual size of a plant, as attested to by my 10-year-old ‘Liberty’ apple tree, topping out at 8 feet high thanks to the M27 dwarfing rootstock onto which it’s grafted. Some rootstocks promote quicker bearing, or tolerance to soils that are too wet, too dry, too salty, or nematode-infested.
Beyond using a small rootstock to make a new tree, another reason for why we graft trees is to makeover an existing tree — as when I cut back pear trees. Topworking can change a white-flowered dogwood into one with pink flowers, or can create a multicolored flowering tree. Or, it can spawn a fruit tree bearing more than one type of fruit, either for more varieties or for cross-pollination without the need to plant another tree.
Plants in the same species are almost always compatible: apple grafts readily onto apple, pear onto pear, sugar maple onto sugar maple, etc. Grafts are sometimes successful between different species within the same genus — so paperbark maple (Acer griseum) can be grafted onto sugar maple (Acer saccharum) stock. Plum and peach (both species of Prunus) are close enough kin to graft together, as are pear and quince (close kin even though different genera, Pyrus and Cydonia respectively), so you can get trees that grow multiple fruits. Never apple and maple, though, nor apple and pear.
Intimate contact must be maintained between the cambiums — the green growth layer located just beneath the bark — of stock and scion. When brought near each other, cells of the stock and scion in this region divide and — if kept immobile by being bound with string, tape, grafting rubbers, or Parafilm — they knit together to establish vascular connections.
New cells that form at the graft union are thin-walled and very susceptible to drying out, which must be avoided. The kneaded mix of wet clay and dung that was used in the 16th century to seal grafts is replaced today by more conveniently applied TreeKote Tree Wound Dressing, Trowbridge’s Grafting Wax, Doc Farwell’s Grafting Seal, and other grafting sealants.
How to Collect Scions
I’ve grafted fruit trees with a Swiss army knife, an X-ACTO knife, and, best of all for its single bevel and straight edge, a grafting knife. The blade must be razor-sharp to make clean cuts, which heal more quickly.
Given the simple conditions needed for a successful graft and the amount of time that grafting has been practiced (going as far back as 1000 B.C. in China), it’s no wonder that so many methods have been devised. The following three common grafts — the whip graft, the cleft graft, and the bark graft — are suitable for “making” or “making over” a wide range of trees and shrubs. The graft you choose should mostly depend on the size of your rootstock or the branches of the tree being grafted. Scions are 1/4 to 1/2-inch in diameter.
Collect scions in autumn after leaves have fallen, or in winter when the temperature is above freezing. Select last year’s stems that are about 1/4- inch in diameter, at least two buds long, and preferably without flower buds. Bundle them into a plastic bag wrapped in a wet rag, and then slide them into another plastic bag, well-sealed to prevent drying. Keep scions in cold storage until you’re ready to graft — the bottom of the refrigerator works.
These three grafts are best completed in late winter, with rootstocks just awakening. It’s best if a scion is dormant at the time of grafting, so that it doesn’t begin growing before it knits to the rootstock.
How to Whip Graft Trees
Whip grafts are suitable for rootstocks similar in diameter to scions, so they’re useful for propagating new trees or adding a branch or two of another variety to an existing tree. Begin this graft by cutting off the bottom of the scion to a long, sloping bevel 1 to 2 inches long, with a similar cut at the top of the rootstock. A single stroke with the knife will ensure a smooth surface for good contact with its mate, though I admit to sometimes touching up the cut. (See photos above.)
Line up cambiums of rootstock and scion — just one edge if stock and scion differ in diameter — and wrap the graft with binding material as you hold the stock and scion in place. Seal the graft (Parafilm Grafting Tape binds and seals). Once a graft is growing strongly, cut a vertical slit into the binding to prevent it from choking the plant.
How to Cleft Graft Trees
The cleft graft joins scions to rootstocks (or branches of a tree) 1 to 3 inches across, so it’s useful for topworking. Use two scion pieces for each graft to hedge your bets in case one of the scions doesn’t take. At the base of each scion, make two bevel cuts less than halfway through the scion, each 2 inches long and not exactly on opposite sides, so that, viewed head-on and from below, the uncut portion is slightly wedge-shaped. (See photos above.)
Prepare the rootstock by sawing it off squarely where you want to graft. Cleave open the top couple of inches of the stump by hammering the blade of a heavy knife into it. Then, remove the knife and pry the cleft open with a screwdriver or similar instrument.
Slide the cut ends of the two scions into the cleft on opposite sides of the stock, with the smaller sides of the wedge cuts facing each other and the cambiums of stock and scions aligned. Releasing the screwdriver will allow the pressure of the stock to hold the scions in place. Coat all cut surfaces with sealant.
How to Bark Graft Trees
The bark graft is my favorite graft for tree makeovers because it comes with the largest insurance policy. Onto a stub of a trunk a couple of inches or more in diameter, stick three, four, five, or even more scions, depending on the diameter of the trunk. Only one scion needs to grow, but the more you graft, the greater your chance of success.
Prepare a scion for a bark graft with a long bevel cut 2 inches long, at its base, almost all the way across the base. On the opposite side of the base, nick off a short bevel. Cut the rootstock trunk completely or cut back some large limbs to stubs. Make two vertical cuts along the bark, each about 2 inches long and spaced the thickness of the scion apart, and then peel back the bark flap to accept the scion, its long, beveled side inward. Prepare and insert other scions similarly, all around the cut surface. When finished, hold flaps in place against scions with a staple gun or a tight wrap of electrical tape. Finally, seal all cut surfaces.
Trees that Grow Multiple Fruits
After you complete any one of these grafts, you can’t just walk away and expect success. When grafting fruit trees, always check your grafts the following day and reapply sealant, as needed. The year following a cleft or bark graft, reduce “takes” to the single, most vigorously growing scion.
Today, I lopped the ends off some major limbs of a 16-year-old chestnut seedling and grafted ‘Liberty’ chesnut on one large stub and ‘Colossal’ chestnut on the other. Tomorrow, I’ll do the same to a ‘Doyenne de Juillet’ pear whose only claim to fame, here at least, is that the fruit ripens in July, and I’ll also graft some ‘Beurre Superfin’ pear scions onto the waiting stub. No harm done.
Lee Reich is a garden and orchard consultant and the author of Grow Fruit Naturally. His “farmden” is a test site for innovative techniques in soil care, pruning, and growing fruits and vegetables, and for hosting educational workshops.