An avocado tree (Persea americana), hardy in U.S. Department of Agriculture plant hardiness zones 9 through 12, can be grown from a seed taken from a grocery store avocado and may produce fruit eventually. After putting in five to 13 years or more of watering, fertilizing and pruning, even if the tree blooms and produces fruits, the avocadoes are likely to be different than the original fruit or, in a worst-case scenario, inedible. Most avocados grown for your kitchen are hybrid cultivars, so any tree grown from the seed will be genetically different than the original tree that produced the fruit.
The new tree will, however, may be a good base for grafting branches from an existing avocado tree that's producing reliable fruit. This will be your rootstock. Once you've grown your seedling to a height of about 3 feet, it's time to graft an avocado tree branch onto it to produce avocado fruit in a process called topworking. Grafting is best done in the spring.
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How to Graft an Avocado Tree to Produce Avocado Fruit
Step 1: Sterilize Your Tools
Dip the blades of your cutting tools in rubbing alcohol or a household cleanser, like Lysol or Pine-Sol, and allow them to air-dry. Also put on safety goggles and gloves before preparing to graft an avocado tree onto a sturdy rootstock.
Step 2: Prepare the Rootstock Plant
Cut off the top of your rootstock plant, leaving at least 15 inches of stem. Make a downward cut through the center of the exposed stem to a depth of 1 inch.
Step 3: Prepare the Scion
Select a cutting from another avocado tree, which is healthy and productive, to graft onto the homegrown tree. This is called the "scion," and it will be the fruit-bearing part of your new grafted tree. Cut a 6-inch length that has several nodes from a healthy branch tip, using a sterilized sharp knife or pruners.
Turn the cutting upside-down (with the cut end up), and cut the blunt end into a point by slicing upward into the stem on both sides to form a wedge shape.
Step 4: Insert Scion Cutting Into Rootstock
Gently press the wedge-shaped end of your cutting into the cut you made on the rootstock stem, aligning the cut ends together to make good contact with each other.
Step 5: Secure the Graft
Secure the grafted section with a cut rubber band or grafting tape. Wrap the joined section with plastic wrap or parafilm from below the union to above it to encase the graft completely, and secure the wrap with grafting tape or cut rubber bands to close the loose ends.
Step 6: Care for the Grafted Avocado
Although avocado trees prosper in full sun, be sure to keep your grafted plant in a shady location until it heals and begins growing. Keep it well-watered to promote healing of the graft union, but avoid fertilizing it during this post-graft window. After four to six weeks, the union should have healed. Gently remove the wrappings and tape, and make sure healing is complete; if not, rewrap it.