Propagating by grafting

In its most simple form, grafting is the process of cutting a branch off one tree and joining it onto the roots of another. The branch is referred to as the scion and the roots (and other parts of this plant) are called the rootstock.

If we use scion from a fruit tree that has a delicious flavour and is disease resistant, and we graft it onto the rootstock of a plant that has vigorous growth and a compact form we'll grow a plant that has the benefits of both plants.

It should be noted that the rootstock and scion must be compatible. In other words, you can graft a pear scion onto the rootstock of a different variety of pear, but you can't graft a pear scion onto the rootstock of an apple, and vice versa. However, there are some exceptions to this rule, for instance quince (Cydonia oblongata) is a common rootstock for pears and loquats. You may like to read Rootstock compatibility for different types of trees at Forest Garden for more information about rootstock scion compatibility.

In commercial orchards, orchardists will generally buy rootstock from specialist growers. Once these have been established in the orchard, they take scion from their preferred trees and graft these scion cuttings onto the rootstock. Alternatively, it is possible to buy scion wood from specialist growers.

Grafting of fruit trees should be carried out in later winter to early spring, when the sap in the tree is starting to be transported, but before flower buds swell.

Rootstock varieties

The form (size) of the grafted tree is primarily determined by the rootstock. Generally, you can buy rootstock in dwarf, semi-dwarf, standard and tall varieties. Standard and tall varieties are more suitable for commercial orchards which have access to equipment for harvesting fruit at height. For home and community gardens, dwarf or semi-dwarf varieties are probably more suitable.

That said, even large form varieties can be pruned and trained to be smaller, but this may require considerable effort and time.

Size is only one characteristic of rootstock variability, take a look at the following webpages to learn more about rootstocks available in Aotearoa:

• Waimea Nurseries: About apple rootstocks
• Genesis Nurseries: Rootstock overview – covers apples, cherries, plums, apricots, pear
• Wairere Nursery: Rootstocks - covers plums, peaches, nectarines, apples, pears, quinces, citrus, avocados, and other species.

Can you imagine a tree that can produce both peaches and almonds? It's not science fiction.

This image might seem fantastical but it is inspired by a living tree. By the end of this topic, you will have an understanding of how contemporary artist, Sam Van Aken, created a single tree that could produce a fruit salad.

The main types of graft unions (the location where the two plant parts join) can be categorised as:

Within each category, there are several different techniques; additionally other approaches exist, such as inlay grafting or approach grafting, but these are outside the scope of this programme.

Overgrafting and regrafting

Two other approaches exist which are worth a mention: overgrafting and regrafting. They may use any of the graft union types described above.

Overgrafting is a technique used in plant propagation that involves grafting a scion (the part of the plant that contains the desired traits) onto a rootstock that has already been grafted with another scion. In other words, it is the process of grafting a scion onto a plant that is already a product of grafting.

An example of overgrafting would be to graft peach scion and nectarine scion both onto an apricot rootstock. Each graft would be attached directly to the rootstock.

In regrafting, a new scion is grafted onto an existing plant that has already been grafted. This technique is typically used to change the variety of a grafted plant or to replace an old or diseased scion with a new one.

Regrafting involves cutting off the old scion and making a fresh cut on the stem of the plant. The new scion is then grafted onto the fresh cut, forming a new graft union between the two pieces of plant tissue.

Regrafting is typically used in fruit tree propagation, where it is often more efficient to graft a new scion onto an existing tree rather than starting a new tree from scratch. For instance, if you have a large apple tree that is in good condition but is disease-prone, you could regraft a disease-resistant variety onto the old scion wood and once it has started growing vigorously you could remove all of the old branches. This way you've been able to grow a new variety on a tree that has a large root system.

In common use, growers may use the term overgrafting when they are actually talking about regrafting, so if in you're unsure ask if they're grafting onto the rootstock of an already grafted tree (overgrafting) or grafting onto the old scion (regrafting).

Watch the following video by National Geographic (4:05) which describes the work of Professor Sam Van Aken, who has grafted trees with 40 different varieties of stone-fruit. While this is not particularly practical, it does show how far you could take overgrafting and regrafting if you wanted to. Not to mention the artistry involved.

Tools and products

For most grafting techniques you'll need the following:

• Secateurs – a pair of sharp bypass secateurs.
• Grafting knife – a sharp knife for cutting bark and wood. While there are specially designed grafting knives, a sharp craft-knife/box cutter will also work.
• Grafting tape – a protective tape that is used to hold graft unions together while they heal.
• Grafting wax – may be applied to tree wounds (such as the top cut of the scion) to reduce the amount of moisture lost from the section.
• Detergent spay or solution – for cleaning pruning tools.

Making a whip and tongue graft

One of the most common types of apical grafts is the whip and tongue.

Watch the following video where Caleb, TheKiwiGrower, walks us through the whip and tongue graft using three different apple varieties. He goes on to show the grafts at 3, 6, and 9 weeks (about 2 months) after grafting and again at six months.

We also recommend that you read page 116 of the Plant Propagator's Bible for another good overview of how to carry out a whip and tongue graft.

Grafting using an omega-cut grafting tool

If you plan on doing a lot of grafting, you might like to consider buying a grafting tool, such as the Pillar Tools Omega-Cut Grafting Tool Kit.

Propagation and maintenance notes

• Do not over-tighten grafting tape.
• Remove grafting tape once the graft union has healed fully.
• Remove shoots from the rootstock on a regular basis. If left to grow they may take away a significant portion of the nutrients intended for the scion, and in some cases may outgrow the scion completely.