Grafting is an ancient horticultural technique that involves physically joining two separate plant parts so they grow together as a single organism. For apple trees, this process is necessary because seeds rarely produce fruit identical to the parent tree, meaning the desirable characteristics of a specific cultivar must be maintained through asexual propagation. The upper part, called the scion, determines the fruit variety, while the lower part, the rootstock, controls traits such as disease resistance and overall tree size. By joining a known scion variety to a selected rootstock, growers can precisely control the resulting apple tree’s characteristics and ensure varietal fidelity.
Essential Materials and Optimal Timing
Successful grafting depends on precise timing and preparation, beginning with the two plant components that will be joined. The scion wood, which is one-year-old growth from the desired apple variety, must be collected while the parent tree is fully dormant, typically in late winter before any bud swell occurs. This collected wood is then stored under refrigeration to keep it dormant until the rootstock is ready for the union.
The rootstock, the established base of the future tree, is ideally grafted just as it begins to break dormancy in early spring, signifying the movement of sap and active growth. The necessary tools include a very sharp grafting knife to ensure clean, smooth cuts that maximize contact between the tissues. Specialized grafting tape or rubber bands are used to hold the components firmly together under pressure.
A sealing compound, often grafting wax or specialized paint, is needed to cover all cut surfaces and prevent desiccation. The diameter of the scion and rootstock should ideally match to allow for maximum alignment of the cambium layer. This thin, growth-producing tissue just beneath the bark must be perfectly aligned for the graft to be successful.
Step-by-Step Guide to Common Apple Grafting Methods
The whip-and-tongue technique is generally preferred when the scion and rootstock are of similar, smaller diameter, such as the thickness of a pencil. The process begins by making a long, smooth diagonal cut, approximately one to two inches in length, near the base of the scion wood and the top of the rootstock. These matching cuts ensure a large surface area for the vascular tissues to connect.
Next, a small secondary cut, known as the tongue, is made downward into the center of the diagonal cut on both pieces, stopping halfway through the initial slope. The scion and rootstock are then slid together so the two tongues interlock, creating a mechanically strong and stable connection. The objective is to align the cambium layers of both pieces perfectly on at least one side, as this is the tissue responsible for generating the callus bridge that heals the wound.
The cleft graft is employed when the scion must be joined to a significantly wider rootstock or a large established branch. The rootstock is cut horizontally, and a vertical split or cleft is made in the center of the stub, typically two to three inches deep. A wedge is temporarily placed into the cleft to hold the split open for scion insertion.
The scion wood is prepared by cutting its base into a long, sharp wedge shape, ensuring the wedge is slightly thicker on the outside edge than the inside. Two prepared scion wedges are usually inserted into the single cleft, one on each side, with the thicker edge facing outward. This outward pressure ensures maximum contact with the rootstock’s cambium layer as the wedge is removed. Cambium alignment is paramount, often requiring the scion to be positioned slightly inward from the rootstock’s bark edge.
Once the scions are placed, the temporary wedge is removed, allowing the rootstock’s pressure to firmly grip the scions. Both methods require immediate securing with specialized tape or rubber bands, wrapping tightly to exclude air and maintain constant pressure on the union.
Ensuring a Successful Union: Post-Graft Care
Immediately after the graft is secured with tape, all exposed cut surfaces must be covered with grafting wax or a sealant compound. This application prevents the rapid drying out of the delicate tissues and acts as a barrier against bacteria and fungal spores. Ensure the top tip of the scion wood and the entire perimeter of the graft union are sealed completely.
Following the procedure, monitoring for signs of success and failure begins, usually within a few weeks. The first positive indication is the swelling and eventual break of buds on the scion wood, signaling that water and nutrients are successfully moving across the new union. Conversely, signs of failure include the scion wood shriveling or turning black, often due to desiccation or poor cambium contact.
As the season progresses and the union begins to heal, it is important to manage any growth that appears below the graft point. Shoots, known as suckers, originating from the rootstock must be promptly pruned away, as they compete for resources and can compromise the desired characteristics of the scion. The binding material, whether tape or rubber, should be left in place for six to twelve months until the callus tissue has fully hardened and the union is strong enough to withstand wind and handling.