When to perform cleft grafts?
Slit grafting is usually made at the end of winter, when the trees begin to bud. However, the ideal period may vary depending on the region and tree species. Thus, in the mountainous regions, it is necessary to wait until spring is installed to carry out the graft, that is to say in the month of April, because at altitude, the rise of sap is later.
This rise of sap occurs at different times for each species. For the almond tree and the lime tree, the graft must be carried out in February, for the spruce and the quince tree, in March and for the currant tree and the cherry tree in April.
Some species, including stone fruit trees such as cherries, apricots and plums, can be grafted in late summer.
The choice of rootstock and scion
You can perform slit grafts on rootstock with a diameter ranging from 1 to 15 cm, even if it is advisable to carry out this type of graft only on rootstocks whose diameter does not exceed 5 cm to be sure of taking the graft. Thicker rootstocks give better results if two or more scions are grafted, but using other techniques, such as crown grafting. These thick rootstocks produce, in fact, too much sap for a single graft.
The grafts must, for their part, be prepared in January and carry, at the time of the graft, several buds.
The stages of slit grafting
To graft properly, get the necessary tools : a pruning hook, a saw, a grafting stick, an iron or wooden wedge, flexible ligatures and grafting mastic.
Then follow the next steps for a successful cleft graft.
Prepare the rootstock
Realize a horizontal and clean cut on the rootstock using a saw. The wound should be located at a height suitable for the type of tree. Then pare the cut using the pruning knife so that it is clean and smooth. Then split the rootstock in the middle using the pruning hook or a hammer and spread until the split is 5 to 10 cm deep.
Insert the wedge for hold the slit open and press or tap gently to make it permanent.
Prepare the graft
Trim the graft just below one eye making sure the cut is clean and shaped like a triangular bevel on both sides of the eye. The side that should face inwards should be thinner than the one that should face out so that the slit is not too far apart when the graft is inserted. Then cut the graft on its other end, keeping three eyes.
Insert the graft into the slot
Insert the graft into the slot ensuring that its cambium is in contact with that of the rootstock. Place it so that its lowest bud faces outward and angle the scion to firm its contact with the rootstock.
Then remove the wedge, holding the rootstock with one hand.
Ligate the graft
Tighten the graft with flexible ligatures such as raffia or a special grafting rubber band and apply the grafting putty to all the wounds. You can replace the putty with clay contained in a fabric pocket and fixed on the wound with raffia.
Note that if the rootstock is thick enough, you can do a double slit graft, but eventually you will only have to keep one scion, the one that flourishes best and fastest.