Some plant varieties cannot be reproduced by layering, by cuttings, or even by seed. Others are unable to acclimate independently to certain substrates. Whether it is to multiply these plants or allow them to live in good conditions, it is necessary to resort to grafting. For example, certain conifers, vines, many ornamental shrubs and all fruit trees, including citrus fruits, are concerned. A minimum of experience in the field is essential and a good knowledge of the possible techniques is preferable for successful transplant on plants. Let’s do a check in.
Principle of a plant graft
The graft consists of using a plant support with roots, capable of feeding a portion of another plant element by providing it with the sap essential to its development. The support plant is called the rootstock and the implanted fragment is called the graft. The best example is that of the rose which is grafted onto the rosehip.
To be able to be grafted, a plant must have tissues that can fuse together. This is exclusively the case of dicots. It is also necessary to respect the following points for a successful union between rootstock and scion.
- Use only perfectly healthy plants to eliminate any risk of contamination.
- Disinfect the grafting knife or grafting knife and any other tool beforehand.
- Select plants belonging to the same botanical genus or at the same family because the graft can only take if there is a physiological compatibility between the two elements.
- The inner bark or cambium of the scion and the cambium of the rootstock must absolutely coincide, i.e. be in contact to allow fusion. This can only be done at the level of the cambium since it is made up of very specific cells that proliferate continuously. If we are content to make the rhytidome (namely what is commonly called the “outer bark” of the two plants) the welding cannot take place.
- Carry out the grafting at the right time, knowing that this is assessed on a case-by-case basis. At the end of winter, in spring, even during summer or even at the beginning of autumn: everything depends on the variety concerned. To avoid making any mistakes, the gardener has every interest in being well informed about the particularities of the species he wishes to graft in order to choose the most favorable time of the year.
- Choose the appropriate type of graft, namely by approach, crown, cleft, crest or even veneer.
It is not unreasonable to consider plant grafting as a surgical procedure since it consists of inserting the tissues of one plant into another so that the two plant elements then become one.
Approach grafting
This is by far the type of plant grafting that guarantees the best results since scion and rootstock continue to be nourished by their respective root systems until the welding is effective. Approach grafting takes place as follows.
- Plant the rootstock plant in a pot so that it can be as close as possible to the mother plant from which the graft will be taken.
- Remove a strip of bark from the shoots of the year of the two elements to be grafted together.
- Ensure that these shreds are strictly of the same dimensions so that once applied one on the other, the notches coincide absolutely.
- Tie tightly, contact between the cut areas must be maintained continuously.
For a graft by approach started in the spring, it is advisable to wait until November to proceed with the weaning. This consists of making a cut in order to release the scion from the mother plant. With a very sharp secateurs, it is therefore advisable to cut below the welding point for the graft and above the welding point for the mother plant.
The adjustment between generating areas is unquestionably the only major difficulty with this type of transplant. If it is not precisely carried out, it can therefore be the cause of a failure. A minimum of experience and good dexterity are essential for this grafting to succeed.
The crown graft
This technique should only be performed on plants in full sap which have leaves and whose rhytidome peels off easily. The best time is in April and May. However, the removal of the graft must be carried out during vegetative rest, that is to say in winter. While waiting to perform the graft, the graft must be kept at a temperature of 2 to 4°C, so it can be in a refrigerator.
The crown graft does not pose no particular difficulty, and many amateur gardeners use it to multiply fruit trees thanks to a small-diameter rootstock grown in the ground or in containers.
The procedure goes as follows.
- Prepare the rootstock by topping it generously up to 20 cm from the ground and pruning it so as to keep only the trunk thus rid of its branches and lateral branches.
- Bevel the graft at the level of the lowest bud and remove the rhytidome only on one side.
- Make a vertical cut on the rootstock, making sure that it is of equal length to that of the bevel of the scion, then take off its rhytidome.
- Insert the scion where the outer bark of the rootstock has been peeled off.
- Bind the two parts.
- Place a putty on the wounds.
If the crown graft is successful, the regrowth of the graft is possible after 15 to 20 days.
The cleft graft
Cleft grafting takes place at the beginning of spring because at this time of the year, the resumption of vegetation is imminent. To perform this type of graft, it is necessary to have a handsaw and a pruning hook. The first is useful for section first the rootstock horizontally and the second serves to perform a lunge which, depending on the diameter of the rootstock, can measure from 4 to 6 cm.
Again, it is necessary to make the cambiums coincide of the rootstock and the graft(s) as exactly as possible for the graft to take. Of course, the ligature is essential. Ideally we opt for links in natural material such as raffia for example.
Note that it is possible to position two grafts at the stitch. They must have been taken in January from the mother plant using a double bevel cut and each have at least three eyes. While waiting to graft them, it is important to bury them for 75% of their height in an area of the garden facing due north and sheltered by a low wall. The aim is to delay their resumption of vegetation compared to that of the rootstock. It is fundamental to respect this point, certainly the most important because it is the guarantee of success of a cleft graft.
The crest graft
The best time to perform an escutcheon graft is in the summer, although specialists sometimes perform it in the spring, but it is more complicated then. It is ideal for roses and can also be used to multiply certain fruit trees.
Equipped with a grafting post, the gardener take an eye on a twig. It is this eye that will serve as a graft. It is then necessary to carry out on the rootstock a incision en T whose lips are gently parted in order to be able to insert the eye or crest. All that remains is to lay a kind of raffia bandage as a ligature so that the rootstock and crest are in perfect contact with each other.
All you have to do is wait between 14 and 21 days to find out if the transplant is resumed. Success leads to the fall of the petiole after it turns yellow. On the other hand, success is not achieved when the petiole turns black then dries but remains in place.
Veneer graft
This is the technique used when the scion is about the same diameter as the rootstock. We start with bevel the scion then the rootstock is notched quite deeply 4 cm above the collar. Care must be taken to cut into the soft part between the bark and the hardwood. This whitish area is called thesapwood. Then, the two elements are pressed against each other and then well maintained with a ligature.
Very young conifers in containers and evergreen shrubs in pots can be propagated thanks to the veneer grafting which can take place, depending on the species grafted, in the spring or during the last part of the summer.