Grafting apple and other fruit trees allows one to combine different varieties and even species to create your perfect tree. It’s mainly used in fruit tree production, whereby varieties are added to rootstocks chosen for reliability and other traits.
- Scion: a twig with leaf buds. Scions are selected for their decorative properties not limited to fruit, leaves, and foliage.
- Rootstock: a plant with a healthy root system onto which a scion is grafted. Usually, just a stump, rootstocks are selected for their interactions with the soil which can affect a tree’s drought, pest and disease resistance, cold hardiness, time to fruit, fruit productivity, tree size and to a lesser extent fruit size.
- Cambium: similar to human stem cells, cambial cells transform into specialised cells. Forming a continuous layer, the cambium produces xylem cells towards the central axis of the stem and phloem towards the outside. While the cambium produces different type of tissue around the plant, above ground it produces wood towards the inside and bark towards the outside.
- Cambium Contact: grafts must align as so both the scion and stock’s cambium align.
- Bench Grafting: bench grafting involves attaching a scion to a rootstock. Bench grafting is the main method of tree production. It is also used to propagate mutations and save heirlooms from old trees.
- Topworking: topworking involves grafting a new variety onto a mature tree. Trees are cut down to a stump, with the major limbs removed, or severely cut back. This can be useful if a particular variety is maladapted to your area or if you wish to test a new variety.
- Frameworking: similar to topworking, but less severe, frameworking keeps much of the tree’s existing framework, keeping the major branches, but adding new varieties. This method allows faster recovery with a return to fruiting within 3 years.
What is Grafting?
Grafting involves inserting a twig with leaf buds (a scion) into a stem, trunk or branch with the scion becoming part of the plant. Grafting is usually used to combine a rootstock (selected for certain characteristics) with a scion (selected for certain characteristics), although can also be used to add multiple scions to a single tree, or even change the variety of a tree entirely.
Grafting is the main method of fruit tree production, and indeed the method that makes large scale production possible.
Firstly, like humans, most fruit trees exchange chromosomes to produce offspring, and therefore will not produce offspring that are true to type. Thus a seed of a Cox apple will produce an apple tree, but not a Cox apple tree, but an entirely new variety. Thus Cox apple trees need to be produced through vegetative cloning, taking a cutting from another Cox.
Secondly, many varieties are difficult to propagate due to a whole host of reasons ranging from poor disease resistance to a lack of hardiness. Hence, they need to be grafted onto a reliable rootstock, often selected for its excellent disease and pest resistance. Similarly, many trees grown on their own roots will grow too large for the average garden, and thus need a dwarfing rootstock, which will reduce the above ground growth. Growing small trees is especially important for fruit production as it allows easy harvesting and economical use of space.
Lastly, and most interestingly, grafting allows one to create custom trees.
Ever wanted an apple tree that could produce fruit six months of the year, with all your favourite varieties? It’s possible!
Ever wanted a tree that could produce apricots, cherries, nectarines, and plums. It’s possible (albeit difficult)!
Ever wanted a heart shaped tree that you can show to your one true love? It’s possible (albeit cheesy)!
These are just some of the advantages to learning grafting, but the benefit is that if you ever get bored of a particular variety, you can chop off some branches and create an entirely new tree.
Sadly, there are limits to what can be grafted. Plants that are too dissimilar will not be able to exchange nutrients, water and glucose causing the death of the scion. Hence as the genetic similarity becomes more and more remote, the less likely a graft is to take. In addition, some species, such as apples, have excellent compatibility between varieties, while others do not.
Plants within the same species can usually be grafted. For example, both the Cox and Bramley varities of the Malus domestica species are compatible.
Plants with the same genus are often compatible. For example orchard apples (Malus domestica) are compatible with crabapples (such as Malus floribunda).
Some plants of different genera are compatible, although plants of different families can’t be grafted.
Selecting & Storing Scions
Scions should be harvested when trees are in dormancy, which occurs from late-autumn to early-spring. They should be stored in the fridge or cold storage to stop them drying out and are best left in damp sawdust, well wrapped in a plastic bag, and clearly labelled. Leaving scions in water will cause them to rot and high temperatures can cause them to come out of dormancy. While scions can be kept for a long time, harvesting late-winter is recommended, reducing the time in storage.
One year old wood (last year’s shoots) is most suitable for grafting, although two year old can take as well. One year old wood can be identified by smooth bark and dormant leaf buds. The break between one and two year old wood is often marked with a bump. Trees with long shoots are worth selecting. Good spacing between the buds and extra-girth make the best scions.
The size of the scion is dependent on whether you are bench grafting, top working or frameworking. For the former two, the length of a pencil with 3-4 buds is optimal, while frameworking 7-9 buds is ideal. This is due to the fact that the first few buds will eventually turn into branches, which is unnecessary, as with frameworking you already have major branches; you are interested in adding fruit buds or short fruiting laterals, which the buds further from the graft will transform.
In order for a graft to be successful, the branch or trunk the scion is to be attached must be in a stage of growth in order to transfer nutrients and water to the scion, otherwise it will dehydrate and die.
Key to successful grafts is ensuring cambium contact, which ensures quick establishment and effective union. The cambium is a layer that produces the other cells, forming callus tissue over the graft and simulating new tissue growth. During growth periods, the cambium can be seen as a thin green line between the wood and bark.
Knives should be sterilised to prevent infection and must be sharp.
Lastly, grafts must be mechanically sound, so there is no room for the scion to move and cambiums to misalign. Tape, glue, and nails can be used to ensure rigidity, or special grafts can be used to ensure interlocking stems.
Sealant helps prevent infection and water loss and can make binds more secure.
Notes On Frameworking
With frameworking, scions should be added to mature wood, rather than towards the end of a branch. The further down a scion is added, the smaller the resultant fruiting laterals and worst the crop.
If you are to add multiple varieties to a tree, vigorous varieties should be placed lower down the tree and less vigorous higher up. The apical dominance of trees, leads to more growth higher up the tree (towards the apex), giving the less vigorous variety a boost, and balancing out the growth.
Types of Graph
Whip and tongue and saddle grafts are used to attach scions to wood with a similar diameter, while cleft and rind grafts are used to attach scions to wood with a significantly larger diameter. They allow you to make grafts at any point around a tree, although are not the be all and end all of grafts. Providing there is good cambial contact, and the graft is mechanically sound, all sorts of techniques can work.
Whip and Tongue
Whip and tongue is usually used in bench working – grafting a scion to a rootstock. The tongue refers to the horizontal cut made both in the scion and rootstock that makes the graft structurally stable.
With saddle graphs the rootstock is cut into a wedge. The scion is cut as to form a ^ indentation, so the “legs” can saddle the wedge.
Cleft means divided in two, so all you are doing here is cutting a branch horizontally and inserting scions at either end. Cutting horizontally rather than vertically is recommended to prevent the scions falling out. Cleft grafting is usually used for frameworking, which involves adding new varieties to a tree.
Rind is synonymous with bark, so all you are doing here is putting your scion in between the bark and the wood. Rind grafting is usually used for topworking – replacing the variety of a tree. Here you are inserting three scions equally spaced into the main trunk.
Jorge works in the Primrose marketing team. He is an avid reader, although struggles to stick to one topic!
His ideal afternoon would involve a long walk, before settling down for scones.
Jorge is a journeyman gardener with experience in growing crops.