Grafting 101

markyscott

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#1
In another thread I was asked to talk about grafting techniques. I'll share what I know, but I don't claim to be a grafting expert. I've done it a fair amount and with increasing regularity as part of developing trees. In fact with trees like pines, you often have no other choice BUT to graft to correct old, leggy branches. So here goes, but feel free to chime in and offer your experiences or suggest some improvements to the technique. As I said, I'm no expert - just a student of horticulture and bonsai like the rest of us.

And the best grafting quote I know is by Brent Watson - he once said "Of course none of this will mean anything to you until you try it...".

I think what he's saying is that grafting is pretty easy to explain, but pulling it off successfully takes a practiced hand. So probably the best advice I can give you is to go out and try it.
 

markyscott

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#2
Let's start with why you might want to graft. There are several reasons:

  1. Reason #1 is to keep cultivars true to type. Want to propagate that beautiful corking bark or dwarf foliage? The only way to be sure is by grafting - seeds may not be true to type.
  2. Reason #2 is to improve the foliage. Have a black pine that you wish had that beautiful Kotobuki foliage? Well you can have it, but you'll need to graft.
  3. Reason #3 is to improve ramification or make the branches more compact. Do you have an old branch that is lacking taper and has no branches close to the trunk? Welcome to the club! But don't count on back budding on that conifer. Grafting may be your only option.
  4. Reason #4 is to change the hardiness. I've often lusted after those beautiful yamadori Ponderosa Pine. But growing one in Houston can be a problem. Well in truth, I can have it. But I might be better off grafting black pine foliage onto that yamadori trunk.
Anyway, those are the four biggies, at least as related to bonsai.
 

markyscott

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#3
A caveat about WHY we might want to graft is WHY NOT graft. To graft successfully, both the rootstock and the scion must be healthy and growing well. Grafting onto a weak, unhealthy tree WILL NOT work. It is not a technique to restore health. It's a technique to do 1-4 above. So start with healthy plants.
 

markyscott

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#4
When you read about grafting, there are about a million names for different kinds of grafts. It makes you think that there's a dark art to it all. But in fact, all the different types of grafts I'm aware of fall into two broad categories:
  • Detached scion grafting
    • In this type of graft, a section of the shoot of is seperated from the parent tree and grafted to the apex or side of the rootstock. The seperated shoot (called a scion) does not have it's own roots. I use this primarily for pines and junipers.
  • Approach grafting
    • With this type of graft, the roots system of the scion and the shoot system of the under stock are not removed until after the graft has taken. So in this case the shoot has roots until the graft has taken. I use this kind of graft for all sorts of trees.
We'll talk about detached scion grafting first.
 

markyscott

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#5
There are all sorts of detached scion grafts, defined mostly by the type of cut that is made to attach the scion to the understock. I think that there are a bunch of specialty tools out there to make the each of the different cuts. The only one I've ever used for this type of graft is called a "side cleft graft", but the name is not all that important. Here's a picture of what a successful graft of this type looks like:

IMG_5812.JPG

See? You cut the scion into a wedge shape and insert it into a cut on the understock. On the one hand, that's all there is to it. On the other, it's really tough to get it right and some steps you can take to improve your success rate and make the graft less apparent when it's done. I'll share what I know about how to do it.
 

markyscott

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#6
For successful grafts:
  • The rootstock and the scion must be compatible.
    • Distantly related plants, such as an oak and an apple, cannot make a successful graft combination. Grafts are usually made using the same species
  • Pines are an exception - there is a wide range of species compatibility. You can graft black pine foliage onto a ponderosa understock, for instance. Junipers are as well - you can graft shimpaku foliage onto a Rocky Mountain Juniper understock as another example.
 

markyscott

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#7
For successful grafts:
  • The vascular cambium of the rootstock must be held in direct contact with that of the rootstock. The vascular cambium is the tissue responsible for the creation of new xylem and phloem
  • The cut surfaces should be held tightly together
IMG_5814.JPG
 

markyscott

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#8
It's good to take a look at a slice of tree and become practiced at identifing the cambium. Just inside the outer bark, lies the green phloem. Between the phloem and the heartwood is a thin white layer - that's the cambium. The cambium is the only edible part of a tree.

IMG_5816.JPG

See? If you scrape away the outer bark and phloem, you'll find the cambium layer. In many trees you can pull it off in strips.

IMG_5818.JPG
 

markyscott

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#9
Here are a couple of examples on shoots that might be used as scions for grafting:
IMG_5822.JPG
IMG_5821.JPG

It's ver important to be able to identify this on your tree - the vascular cambium on the scion HAS to line up with the vascular cambium on the understock. If the scion and the understock are the same size, it's easy. If the understock is older and larger than the scion, it's a bit tricky to get everything lined up right.

IMG_5824.JPG

See? If the understock is bigger the scion is placed on one side of the stock so that the cambium layers match. On older branches the cork layer might be thickener meaning you can't line up the bark of the understock and scion - the scion will be recessed a little to line up the cambium layers. So you need to be able to identify the cambium so you know how much to recess it from the edge. When Boon does it he estimates and get's it right most of the time. When I do it I look very carefully and miss a lot of the time. It takes practice.
 
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markyscott

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#12
So a couple of other things to keep in mind for successful grafts:
  • The plants must be in the right physiological state.
    • Ideally, the scion is dormant while the rootstock is in spring growth. That way by the time the scion is ready to push buds, the rootstock is capable of sending water across the graft.
    • Second best time is while both the rootstock and the scions are dormant.
    • The worst time is when both the scion and the understock are growing
Do it when it's a bit cold outside, especially for conifers. If the sap is running it could fill the cut before the cambium can callus across the graft - not good
 

markyscott

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#13
Here are the tools of the trade:
  • A good grafting knife
IMG_5826.JPG
The knife should be razor sharp. I use Japanese water stones to sharpen them, finally finishing the edge with a razor strop. I restrop the knives after every few grafts. You want the knife so sharp, that the hairs of your arm will pop right off when you touch them.

A word about handidness with grafting knives - because Japanese grafting knives are beveled on one side and flat on the other, they come in left- and right-handed varieties. The flat side goes toward the trunk. But handedness terms are written for whittlers. In whittling you run the knife away from you. Grafting is often performed by pulling the knife toward you. If this is your practice, buy the opposite kind of knife - right-handed people will often use left handed knives for grafting. If you run the knife away from you, buy a knife with the normal handidness.
 

markyscott

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#15
So first let's talk about cutting the understock. Flat side of the knife against the branch and in one motion, make a smooth even cut into the under stock at the desired graft location.

IMG_5830.JPG

You need good, flat, straight cuts. The cuts should be, as much as possible, a single, straight, smooth stroke. Once you begin making the cut, the knife should not stop moving. The purpose of the flat side of the knife is make a cut that does not tend either to curl in, or curl out of the cutting plane.

Where do you cut? Well, remember, if we're grafting, we're trying to tighten up the ramification. Graft close to a branch crotch, the roots, and/or close to the branch union with the trunk. Don't try and graft way out on the end of the branch - that does you no good whatsoever. Make the cut on the sides or top of the branch, not on the bottom. If you cut into the side, cut the side in the direction you'd like to see the branch turn.

How deep do you cut? Well, you need to go far enough into the trunk to create a tightly closed cut after you withdraw the knife. If you cut too deep the trunk will split or the top will lose its stability. If you cut too shallow, the outside of the cut won't have enough wood to make the graft tight.
 

markyscott

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#16
Now let's talk about cutting the scion:

Picking a good scion is a bit of a trick. Good scions are usually 1/4 inch caliper or less. We cut into two year old wood for the graft - so it should have the green to light brown summer shoot from last season and the woody growth from the previous one. It's the two year-old wood that we'll use to make the graft. I've used a single node (bud or whorl of buds) at the end and I've used a branched scion. For smaller cultivars, the scion is usually cut just above the last node. When the last internode section is very long, a stub can be left, or the scion shortened later. Typically, scions are one to three inches long.
IMG_5831.jpg

See? Like this one. And inspect the terminal bud when selecting scions. A small terminal bud may “take”, but the success rate is higher when there is a nice fat bud at the tip. If there are extra buds around the terminal it's good as they are an insurance policy in case the terminal bud dies. Remember that the node at the base of the terminal bud is going to provide the first branch on the grafted tree, so you don't want a really long stick of a scion; the shorter the better.
 

markyscott

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#17
Lay the scion flat on the block. You want the side to be placed against the tree facing up. Angle it so that the whorl and buds are to one side of the edge of the block. Position the knife and scion so that you are pulling the knife toward you, flat side of the knife down against the scion. Pull the knife through to the bottom of the scion to make a cut that is about 3/4 inches long, and make it go halfway through the scion, thus removing a small U shaped bit of wood from the bottom of the scion.

IMG_5832.jpg
 

markyscott

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#18
To make the scion pointed, turn the scion over and now position the cut you have just made flat against the block.
Now make the shorter 1/4 inch cut by pulling the knife down through the scion in the same fashion, except that this time the knife is going to go all the way through the scion and into the block to make a flat sharp edge to the bottom of the scion. If the edge is not sharp, you will have to repeat the cut, starting at the top again. If you remove too much material, the long side will now be too short, start over.

IMG_5833.jpg

When you're done, pull needles. You only want about 4-6 sets around the bud. More than that will increase the water demanded beyond what the grafted union can provide.
 

markyscott

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#19
In the end you should have something like this:
IMG_5834.jpg

There is a long side of the wedge that should be as long as the inside of the slit on the understock. The gentler the angle on the long side the more cambium is exposed. The short side of the wedge is mostly to make it pointed.