What is grafting?
Grafting occurs naturally in forests when two branches of two different trees (or sometimes the same tree) touch each other, merge, and continue to grow. As a technique used by humans for tree propagation, its use dates back to ancient times in many civilisations.
The earliest definite references to grafting are found in ancient Greek writings, in around the 4th century BCE. It must have begun to be used there hundreds of years earlier, however; since at that time it was already a common practice.
The image to the right shows a mosaic depicting one of the earliest known images of grafting. The image is reproduced with thanks from JF Bradu. Grafting was also practiced in Ancient Rome, Persia and China, and to this day one of the most important tree propagation techniques. When people buy fruit trees, they are almost always grafted; especially apple and pear trees.
But what exactly is grafting?
The purpose of grafting: reproducing identical fruits
Nurseries, breeders and orchardists use the technique of grafting for several different reasons; the first and most important being to produce a plant cultivar that is identical to the original source. For example, let’s say we discover an apple tree which produces apples of exceptional quality.
We will call the apple ‘Honeycrisp’ for ease of explanation. The Honeycrisp apple is so good that we want to create an orchard full of this apple. How do we do this?
Now the first thought we might have is that we could plant the seeds of a Honeycrisp apple and wait for them to grow into trees. The problem, however, is that although these trees will have some characteristics similar to Honeycrisp, they will not be identical and the fruit will not be quite the same.
This happens for the same reason that every human being has characteristics in common with their parents, but is not a carbon copy of them. Apple trees reproduce sexually so that each seed contains a unique combination of genes of more than one apple tree. Therefore, each seed will produce a different apple tree, even the seeds from one apple.
This is why grafting is so important; it allows us to reproduce an exact copy of a specific cultivar like Honeycrisp. Most trees can be grafted, but the technique is most commonly used for fruit trees such as apple, pear and plum.
What exactly is a ‘graft’?
A graft works in a very similar way to a human body-part transplant. Just a kidney can be taken from one human body and inserted into someone else’s body; with grafting we take a bud from the original Honeycrisp tree (called the scion), and link it to the stem and roots of another young apple tree, called the rootstock.
Nature does the rest. Just like the human body accepts and functions with the new organ, the tree trunk and the bud grow together and are unified. The sap from the rootstock travels into the Honeycrisp bud and revives it, and the bud eventually grows to become the new trunk of the tree.
Thus, in reality a “grafted tree” is actually an association between two trees. Below the graft union there is an apple tree that we call the rootstock. The rootstock provides the roots of the tree. Over the graft union, we have the grafted bud, which in this case is the cultivar Honeycrisp. This does not grow by way of its own original roots, but on the roots of the rootstock.
Once a tree is grafted, its fruit is identical to the original tree (in this case Honeycrisp). We can then use the branches of our newly grafted tree to graft even more trees.
When we look attentively, we can see the scar of the graft (the area where the bud has been grafted) on the trunk of the tree. Even after a number of years, the scar of the graft or a clear change in colour is still visible. The photos below show trees that are newly grafted, young trees whose graft union is still obvious, and an older tree where you can still see how the colour of the bark changes at the graft union.
The importance of the rootstock
The rootstock is the young tree onto whose roots we graft the bud from the desired variety. The rootstock influences the tree in several ways; it is the rootstock which will determine the size, vigour and lifespan of the tree, and will also influence its cold-hardiness.
In the case of apple trees, there exist ‘dwarf’ and ‘semi-dwarf’ rootstocks which restrict the size of the apple tree and are therefore popular in commercial orchards.
However, dwarf rootstocks have also significant drawbacks – in particular, they lack cold-resistance, are much higher maintenance than standard rootstocks, and have a very short lifespan compared to standard apple trees.
We explain the difference between standard and dwarf rootstock in detail in this article, as well as our reasons for choosing to graft all our apple trees on standard (full-sized) rootstock that we grow from seed.
Caring for the graft
- Locating the graft union: If your rootstock is cold-resistant and vigorous, the graft does not require any particular care. However, it is a good idea to locate the graft union, if possible. Any branch that grows under the graft union should be removed, as its fruit will be the fruit of the rootstock, not that of the cultivar you are expecting.
- Breakage: If it happens that your tree should suffer breakage, you should check whether the damage is above or below the graft union. If the tree is broken above the graft, you have not necessarily lost your grafted variety; instead the tree will just need to grow a new main trunk from a bud that is above the graft union. On the other hand, if your tree is broken under the graft, it means that the grafted cultivar is lost. The rootstock will continue to grow and bear fruit, but quality of the fruit may not be as pleasing as that from the grafted cultivar.
- Protective spirals: This is also the reason that we provide a protective spiral for every grafted tree. Protecting the trunk of your young tree is more important in the case of grafted trees, since if the graft is damaged, the cultivar can be lost for good; while for a non-grafted tree, even if the main trunk is damaged, the tree can still grow back as before. This doesn’t mean that protecting even a non-grafted tree is not a good idea; many other trees will also benefit from protective spirals. See the complete list here.
Other ways that grafting influences the tree
- Precocity: Grafting influences the time it takes for a tree to produce fruit: grafted trees will produce fruit earlier than non-grafted trees. For example, an apple tree that is not grafted will not produce fruit for about 10 years, whereas a grafted apple tree will begin to bear fruit after 4 years. This occurs because the bud used in grafting is already mature.
- Disease-resistance: Grafting is also used to control some diseases. For example, greenhouse tomatoes are often grafted using a similar technique to that used on fruit trees. Some diseases that affect tomatoes are found in the soil, so using rootstock that has resistance to this disease will allow the grafted variety to have immunity from the disease. This is because only the resistant rootstock will touch the disease-containing soil.
- Grafting is also commonly used in Europe to produce grape vines. This practice began in the 19th century due to an insect called phylloxera that eats the roots of grapevines. European grape vines were badly affected by phylloxera, and it was found that the only way to protect the vines was to graft them onto resistant American vines.
Grafting at Hardy Fruit Tree Nursery
At Hardy Fruit Tree Nursery, we graft almost all of our apple, pear and plum trees. All of our rootstocks are full-sized trees which give the tree a long life and vigorous growth. Most of our rootstocks are hardy for zone 2, allowing them to survive cold harsh winters.
Some apple trees on the market are propagated by layering methods. However we prefer seedlings which allow a tap root to develop, thus providing trees with more stability.