Excitement on the prospect of making a kill by growing avocados is not going away any time soon. Today, I explain the concept of grafting avocados.

Avocado tree grafting involves connecting the branch of an avocado cultivar (the scion) with the rootstock of a different tree. As the two grow together, a new tree is created. The closer the scion and the rootstock are to each other biologically, the better chance you have of successfully grafting them.

Grafting is necessary to obtain a large crop of top quality fruit and can speed up the process of fruit bearing. If you grow an avocado tree from an avocado seed, you’ll have to wait six years before you see any fruit. And even after the seedling grows, there is no certainty that the tree will be look like the parents or produce fruit of the same quality. That’s why it is not advisable to grow avocados by seed.

After removing the avocado seeds from a mature fruit, the seeds are washed and dried to remove the seed coat. Seeds can be germinated either in sawdust or sand, with careful attention to optimum moisture maintenance. Once, the germination starts the root and shoot are transplanted into a planting bag. Grafting starts about six weeks after transplanting.

Selecting grafting wood

Successful avocado propagation requires obtaining grafting wood from branches that have demonstrated high production of true-to type fruit, on healthy, vigorously growing trees. The best wood is on young trees, or older trees that have been cut back severely to force strong upright new growth.

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Select graft wood that is firm and not rubbery or pithy. Each scion cut should have at least two, preferably three or four sound dormant buds. The best buds are large and plump, with a healthy green color. Undersized buds are less likely to survive and grow. However, extra-large buds and plump buds may be flower buds, which produce weaker vegetative shoots or none at all. Buds that are slim and elongate, often with tiny leaf like feathery tips, are not dormant; they will not store well and will take less successfully even when used fresh. Such immature buds have cambium that is more active and so might be considered better for propagation, but they are more vulnerable to desiccation.

How to graft

Grafting is a matter of precision. Position the branch section properly on the rootstock, such that the cambium on the branch and the cambium on the rootstock touch each other. If not, the graft is certain to fail.

Perhaps the most common method of grafting avocados is the cleft graft. Make a vertical split in the centre of the rootstock, then insert one or two branches (scions), with two or three buds, into the cambium layer of the rootstock. Place the rootstock in moist sphagnum moss. It will hold water but also allows for aeration. The temperature should be about 27oC, although the scion must remain cool. Create humidity to prevent drying of the graft union.

Avocado tree grafting is difficult. Even in ideal conditions, the odds of success are low, even for professionals. 

Cut 6-inch lengths of healthy branch tips that each contain several buds, using a sharp knife. Take six to eight cuttings, wrap them in damp paper towels, and lay them in a bowl of ice to keep them cold and moist.

Make a T-shaped cut on a branch of the rootstock tree, about 12 inches from the trunk. The long part of the T should be about 1-inch long. Make a shorter, crossing cut that goes 1/3 of the way through the branch. Twist the knife slightly to pry the bark away from where the two cuts meet. Examine the bud sticks you cut and placed in the bowl. Choose a healthy bud, and cut it from the stick, beginning 1/2 inch below the bud and ending 3/4 inch beyond it. Bring the selected bud back to the rootstock. Slide the long end of the bud wood into the long part of the T-shaped cut, matching the bud to the horizontal cut in the T.

Wrap the budded graft with a rubber band, securing it above and below, but not actually on the bud. Remove the rubber bands when the bud unions have healed and buds begin to open, which should be within three to four weeks. As these new branches grow and mature, avocado fruit will be produced on them.  

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