Apple trees cannot be reliably propagated from seed to produce the same type of fruit, making grafting necessary. Grafting is an asexual method of propagation that joins a piece of the desired fruit variety onto the root system of another tree. This process creates a genetically identical clone of the parent fruit, ensuring the resulting tree yields the expected apples. Combining the two plant parts allows cultivators to control the fruit characteristics while influencing the size and hardiness of the overall tree.
Why Apple Seeds Do Not Produce Desired Fruit
Grafting is required due to the complex genetics of the apple tree, specifically high heterozygosity. This means a named apple variety, such as ‘Honeycrisp,’ carries two different versions of many genes. When an apple flower is pollinated, the resulting seed contains a new, random combination of genes from two parents.
Planting a seed from a named variety produces a genetically unique tree that will not “breed true” to the parent fruit. Most seedling trees revert to a wilder, crabapple-like form, yielding fruit that is small, sour, or undesirable. This genetic lottery makes propagation through seeds impractical for growing a specific cultivar. Asexual methods like grafting are necessary to bypass sexual reproduction and create an exact clone of the fruit-producing portion.
Selecting and Preparing Rootstock
The rootstock is the bottom portion of the grafted tree, providing the root system and lower trunk, and it determines several important growth characteristics. Rootstocks are categorized by the size control they impart, ranging from standard to semi-dwarf and dwarf. Dwarf rootstocks, such as the M.9 series, produce trees that are 30% to 45% the size of a standard tree, which simplifies harvesting and maintenance.
Selecting the correct rootstock also allows the grower to select for traits like disease resistance and soil adaptability. The Geneva series (G-series) is valued for its resistance to common diseases like fire blight and Phytophthora crown and root rot. For example, a semi-dwarf rootstock like Geneva 935 (G.935) offers significant disease resistance while producing a tree roughly 50% to 60% of standard size.
Preparation involves ensuring the rootstock, often purchased as a bare-root whip, is healthy and dormant before grafting. The rootstock should be about the same diameter as the scion material, ideally between 1/4 and 1/2 inch, for the best chance of a successful union. Before cutting, the rootstock is pruned to a manageable height, usually 6 to 10 inches above the root crown, providing a straight section for the join.
Step-by-Step Grafting Techniques
Grafting involves joining the rootstock with the scion, a short piece of dormant wood from the desired apple variety, ensuring the cambium layers align. Scion wood should be collected in late winter or early spring while the tree is fully dormant. The whip-and-tongue graft is a common and successful method for joining materials of similar diameter, creating a strong, interlocking union.
To perform the whip-and-tongue graft, use a sharp knife to make a long, sloping cut (1 to 2 inches) across the top of the rootstock. A small, downward cut, or “tongue,” is then made into the center of the slope. The scion material, typically one-year-old growth with two to four buds, is prepared identically, creating a matching sloping cut and tongue.
The goal is to maximize contact between the cambium layers—the thin, active growth tissue beneath the bark. The cambium layers of the rootstock and scion must align precisely, at least on one side if diameters differ, as this is where healing and fusion occur.
Once interlocked, the union is secured tightly with grafting tape or an elastic material to provide support and prevent drying. All cut surfaces, including the scion tip, should be sealed with grafting wax or pruning compound to prevent moisture loss and infection. The newly grafted tree must then be labeled to identify the scion variety.
Essential Care for New Apple Trees
The period immediately following grafting is important for the formation of the vascular connection, which allows the scion and rootstock to grow as one plant. Newly grafted trees should be kept in a protected area, away from strong winds and intense sunlight, for the initial healing period of about two weeks. Maintaining a cool, moist environment is important; if bench-grafting was performed, the trees can be temporarily potted in moist sand or potting medium.
Monitor the graft union to ensure the binding material remains intact, as movement or drying can cause failure. The first sign of successful growth is the swelling and breaking of the scion buds, indicating that water and nutrients are moving across the new connection. The binding tape should remain on the graft for several weeks or months after bud break to allow the union to fully strengthen before removal.
A continuous management task is the removal of suckers that sprout from the rootstock below the graft union. This new growth competes with the scion for energy and nutrients and must be aggressively pinched or pruned off as soon as it appears. Removing suckers directs the tree’s energy into the scion wood above the graft. For the first year, the goal is to encourage one strong, central leader shoot from the scion.