Chapter 36 Top Grafting and Budding Techniques for Bonsai
Grafting and budding are methods for taking living material from one plant, and moving it to another location on the same plant, or to a new one. In both methods the rootstock and scion are wounded in a way that stimulates their green cambium layers to fuse. Once they fuse, the rootstock provides the water and nutrients the scion needs to grow.
Grafting adds or moves woody parts like branches or roots. Budding adds single dormant buds to existing branches or even the trunk. With care these form shoots that can be trained like any other branch. I have focused on top grafts here; root grafting is discussed elsewhere.
Grafting and budding are not impossibly arcane arts. Follow some basic guidelines and practice the necessary skills in advance, and you likely will succeed. Like root pruning, leaf cutting, or any other technique in bonsai there is a proper time and reason for using it. Done correctly, budding and top-grafting can dramatically improve trees; done improperly, they can leave scars that deform the lines of the trunk or branches.
36.1 Why and When to Use Grafting and Budding
We all have trees with uneven root spread, misplaced or insufficient branches, or a poor apex. Grafts can be used to add branches in exactly the right position, reshape or replace poor branches, create additional nebari roots, or even change the type of foliage a particular tree will have. It is even possible to graft a particular cultivar that has weak rootage but forms good top structure onto “nurse roots” that are more resistant to disease or grow more rapidly. This is a common practice with Japanese maples; many cultivars form poor roots, so the desirable top is grafted onto a stronger seedling rootstock.
On the negative side, grafting and budding are labor intensive. It also is important to weigh the advantages against the possibility of scarring or otherwise damaging a tree. If a problem can be solved with routine methods (wiring, clip and grow, etc.) do not try to solve the problem by grafting. Let the tree correct the problem instead.
36.2 Which Trees Can be Budded or Grafted?
I first learned to graft and bud because I wanted to preserve some heirloom apples, which take well to grafting. However there are many others used in bonsai that can be grafted or budded successfully. Table 1 lists several species, and how easily each can be grafted or budded. Do not try to graft trees that are not the same species. Mixing species or genera (say, a maple top onto oak roots) does not work.
Table 1: Species that commonly are grafted
| Species | Ease of Grafting * |
|---|---|
| Crabapple (Malus sp.) | Very easy |
| Fig, tropical (Ficus sp.) | Very easy |
| Cherry, apricot (Prunus sp.) | Easy |
| Cotoneaster sp. | Easy |
| Elms (Ulmus sp.) | Easy |
| Hawthorn (Crategus sp.) | Easy |
| Hornbeams (Carpinus sp.) | Easy; bark is thin |
| Maples (Acer sp.) | Easy; widely used to propagate cultivars |
| Willow (Salix sp.) | Easy |
| Crape myrtle (Lagerstroemia sp.) | Moderate; watch out for thin bark |
| Euonymus sp. | Moderate |
| Azaleas (Rhododendron sp.) | Prior experience |
| Birches (Betula sp.) | Prior experience |
| Pines (Pinus sp.) | Prior experience; not all species compatible |
| Boxwoods (Buxus sp.) | Difficult |
| Pyracantha sp. | Difficult; brittle wood; use budding only. |
| Wisteria sp. | Difficult; grafts take but dieback is common. |
| Beeches (Fagus sp.) | Cultivation |
| Cedars (Cedrus sp.) | Cultivation |
| Chamaecyparis sp. | Cultivation |
| Hollies (Ilex sp.) | Cultivation |
| Spruces (Picea sp.) | Cultivation |
| Junipers (Juniperus sp.) | Cultivation; prior experience |
* Species marked “Cultivation” are almost entirely propagated for the nursery trade by grafting specific named cultivars onto seedling rootstocks. They should work with whip or cleft grafting, but I was unable to find more specific information about how readily they can be grafted. “Prior experience” indicates that grafting or budding this species can be done with some experience, but should not be your first project.
36.3 When Are Trees Budded and Grafted?
Proper timing is the single most important factor in whether these operations succeed or fail. A few species have unusual requirements, but generally, budding is done while the rootstock is actively growing, and next year’s buds are still dormant but not yet fully hardened; here in North Carolina, the optimum time for budding is early August to Labor Day. Grafting is done in late winter, just as the buds BARELY begin to swell on the rootstock (the name for the main or larger tree). If the buds have broken and green is showing, it is too late for the year. Scions (the fully dormant wood to be attached to the rootstock) are collected in mid-winter, and stored refrigerated.
36.4 How Is It Done?
Successful grafting requires a very sharp knife with a straight edge. Specialty grafting and budding knives are available, but a sturdy pocket knife or single-edged razor blade works just as well. Other supplies include wide rubber bands or cotton string, and some type of non-adhesive plastic tape or sealing wax.
The same general method is used in all forms of grafting. Just before making any cut, the area on the rootstock where the graft will be made is rinsed with plain water, and wiped to remove any dirt or debris. The stored (or freshly collected) scion wood is cleaned the same way. The first cut is made in the rootstock, then immediately a matching piece of appropriately shaped scion wood is cut. An ideal piece of scion wood is 3-6 inches long, has 2-5 healthy looking dormant buds on it, and was collected from last season’s newly hardened wood; older scions tend to fail more often.
When the two pieces have been cut, the scion is pushed into the cut on the rootstock, so that the cambium layers of the two pieces contact each other over the longest distance possible. It is vital NOT to touch either cut surface, since dirt or bacteria from your hands can contaminate the cut, and cause graft failure. It is also important to work quickly, because the live, exposed edges of the cambium dry out and die quickly, again leading to graft failure.
To keep the scion from being dislodged, it is tied in place with either cotton string or a wide rubber band wrapped around the graft union and tied. The graft is more likely to take if the site does not dry out, so it also is wrapped with non-adhesive plastic tape, or sealed with wax. To prevent girdling the wrapping should be removed within 3-4 months, or when the scion buds show strong growth.
Each of the commonly used methods of grafting are described in more detail and shown below. For clarity, the wrapping and tying steps have been omitted. Only the cuts and how they fit together are shown.
36.4.1 Whip Graft, Whip-and-Tongue Graft
Whip graft (1) and whip and tongue graft (2). The primary difference in the two methods is that (in the latter) the scion and rootstock have a second “tongue” groove (A and B respectively in the right panel) in addition to the cut faces (C). When pushed together, the tongues hold the two pieces together tightly (D). Link to image source.
These are the most widely used methods for grafting branches or trunks of approximately equal size. (If the diameter of the scion is 75% or less than the rootstock, use a cleft graft, described below, instead.) For a whip graft the rootstock is cut off at an extremely steep angle, forming a long sloping face about 1 inch long. The scion is cut the same way. The two are aligned so the cambium is in contact over as much area as possible, then the two pieces are tied together and sealed. Whip grafts are simple to make, and for small diameter branches or trees (1/4-inch or less) are more than adequate.
For a whip-and-tongue graft, a second cut is made into the wood of both the rootstock and scion, parallel to the trunk or branch, and 2/3 of the way in from the pointed end. When the rootstock and scion are pushed together, the two “tongues” of wood interlock, and form a tight connection that is less likely to slip than a simple whip graft. Another advantage is that one person can make the graft, then let another complete the tying and sealing. It also does not require you to hold the two pieces together if you are working alone.
36.4.2 Cleft Graft
A cleft graft. Link to image source.
This method is used when the scion is significantly smaller in diameter than the rootstock. It also is a good method for creating taper in a long thick branch, or enhancing the taper of a trunk that is too fat near the apex, but is unlikely to back-bud. The branch or trunk of the rootstock is cut off to create a flat stump, then a heavy knife blade is wedged into the center, splitting the wood. Two pieces of scion wood are cut so the lower ends are pointed, and they are inserted into the cleft in the rootstock. Usually two scions are inserted, to improve contact and in case one of the two does not survive. The cambial layers are lined up, then the union sealed and tied. Very often the growth of the union will round out the shape of the flat graft junction, but if it remains unsightly, it can be trimmed down after a year or two, when the scion is growing well.
36.4.3 Approach Graft
Approach graft. Link to image source.
These grafts are used to connect a smaller tree to a larger trunk. The smaller tree may be providing additional roots, in which case its top will be removed once the graft heals. Approach grafts also can be used to add branches to bare areas; once the graft union heals, the bottom half of the smaller tree is removed and the scion draws water and nutrients from the main trunk. If the smaller scion tree is contributing additional roots, it should be planted in the same pot as the rootstock at least 6 months before the operation. A scion that will become a new branch can be kept in a pot of its own, sitting atop the soil and next to the larger tree. The sides of both the rootstock tree and scion tree are sliced or skinned with a knife or razor to expose the cambial layers, then they are tied together tightly. Compared to whip and cleft grafts an approach graft is slower to take, and is more likely to fail since the scion can survive on its own roots. If the intended junction does not form, simply skin the two trunks and try again. Ficus takes particularly well to it.
36.4.4 Side Graft
Side graft. Link to image source.
These are used to add branches to a bare trunk. The angle of placement can be more accurately controlled than with approach grafts. The basic process is the same as a whip graft, except that a heavy chisel or thick knife is used to slice through the bark on the side of a dormant tree. A pointed piece of scion wood is inserted into the cleft and positioned so the cambial layer matches that on the rootstock. The wound is taped or tied closed.
Side grafts need more after-care than most. Water can pool in the cleft and lead to rot. However, the cleft cannot be packed with wax or emulsion, as this will prevent the cambium from rolling in. Most sources recommend using stretch plastic tape to seal these wounds.
36.4.5 Thread Graft
This method is widely used for adding new branches to bonsai trees. I have not used myself, so I cannot say how well it works. It supposedly only works on deciduous, broadleaf trees.
A hole is drilled through a large caliper trunk, then a thin sapling or branch from the same or another tree is threaded through the hole, so it exits the trunk where the new branch is desired. The holes are closed with sealant and the trunk is allowed to close around the new branch. The grafted branch is not cut free for at least 1 year in most cases; two years is better.
36.4.6 T-Budding
When a bud is cut from the scion, often a long tag of bark from above the bud is torn away with it (A). This long tag can be used as a second “handle” for manipulating the bud. Once the bud is inserted the tag is cut off at the Point “H.” Link to image source..
Nearly all budding is done this way. It is rarely necessary to use other methods. Unlike grafting which is done while trees are dormant, budding requires the bark of the rootstock be able to “slip,” that is, to lift easily from the underlying wood. Also scion wood must be collected fresh on the day its buds are to be grafted. Not all of this season’s growth will have suitable buds. Look for large pointed buds that appear to be mature and healthy, about midway along the branches formed by this year’s growth; most good buds will be at the bases of this year’s leaves. Do not use buds at the branch tips, since they are not yet mature. Cut the entire branch containing the buds from the source, and snip off all the leaves (to reduce drying), leaving a 1/2-inch piece of the leaf stalk attached, to serve as a handle when you cut the buds.
To start, the rootstock should always be cut first. Using a sharp knife, make a T-shaped cut in the trunk or branch of the rootstock where the bud will be placed. Do not cut too deep; it should barely break through the green cambium. The top of the “T” should not extend more than 1/3 of the way around the trunk, and the long part should be no more than 1 inch long. After cutting the T, angle the knife blade so it is parallel to the bark, then gently push it into the cut, so that a flap of bark is pushed up. Be careful not to tear the bark. Flip the knife over and repeat to make a second flap.
Once the rootstock is ready, use a knife to slice under a healthy bud on the scion wood; a correctly cut bud is ~3/4 of an inch long, 1/4-3/8 inch wide, and has a uniformly green edge. Gently lift the bud from the scion using the leaf-stalk as a handle.
Returning to the rootstock, use the knife blade to gently lift up the flaps of the T that was cut earlier. Use the leaf stalk to place the cut bud under the flaps of bark. If done properly, you should be able to push the two flaps back down to cover the bud, leaving just the pointed tip exposed.
Once a bud has been placed it is wrapped with a rubber band to hold it in position (buds are never tied) then covered with plastic tape to prevent drying out. The wrapping is removed after 3 weeks, and if successfully integrated, the bud should begin growing the following spring.
36.5 Why Grafts and Buds Fail
One advantage of grafting and budding is that it is obvious if it works. If the buds of the scion do not swell and open by late spring, the graft likely has failed. The most common cause of graft failure is the cambium layers were not lined up properly. Drying out is another frequent problem. Fortunately most failed graft sites do not die completely. Often a shoot will form that does the job you intended for the grafted scion. Alternatively, try grafting it again next year.
Personally I think that another common problem is that grafting requires a certain amount of dexterity and coordination. Practicing once a year is no way to become proficient. To hone my skills I have started practicing my technique using small branches I cut from maple trees in the yard or woods. If I have a piece of string I even practice the tying step. It costs nothing but gives me greater confidence when it counts.
36.6 For More Information
There are many good books out there; the most comprehensive is The Grafter’s Handbook, by R.J. Garner. It was first published in 1947, but still is the best one-stop resource available. The figures I used for this story all came from the 2003 edition.
Both prior and current editions are available through Amazon.