The process of “cloning” an apple tree refers to asexual propagation, primarily achieved through grafting or budding. This vegetative method is necessary because apples grown from seed do not reproduce true-to-type. A seed from a ‘Honeycrisp’ apple will produce a tree with fruit of different, and often inferior, characteristics due to highly variable genetics from cross-pollination. Grafting bypasses sexual reproduction entirely, creating a genetically identical copy of the desired variety by physically joining two different plant parts, ensuring the resulting fruit is precisely the one intended.
Essential Components for Cloning
Successful cloning requires the careful selection and preparation of two components: the scion wood and the rootstock. The scion is a short length of dormant wood taken from the desired apple variety, containing two to three buds that will form the new tree’s canopy and fruit. This wood must be collected from the previous season’s growth, typically in late winter or early spring while the tree is fully dormant, and stored moist and cool until the grafting process begins.
The rootstock serves as the bottom half of the new tree, providing the root system and anchoring the plant to the soil. Its genetics determine several important factors, including the tree’s ultimate size, cold hardiness, disease resistance, and adaptability to specific soil conditions. Both the scion and the rootstock must be healthy, dormant, and ideally of a similar diameter, generally between 1/4 and 1/2 inch, to maximize the success of the union.
The Grafting Process
The whip-and-tongue graft is the most common method for apple trees, typically performed indoors during late winter or early spring when both components are dormant. This technique is favored because the interlocking cuts create a strong physical union and maximize the surface area for the cambial layers to meet, which is crucial for healing. The process begins by making a single, long, smooth diagonal cut, about one to two inches long, across the end of both the scion and the rootstock.
Following the initial diagonal cut, a second cut, known as the “tongue,” is made into the face of the first cut, slicing toward the base. This tongue cut should penetrate about halfway through the wood and is made identically on both the scion and the rootstock. The scion and rootstock are then carefully fitted together so the tongues interlock snugly, creating a tight, reinforced joint.
The most important step is ensuring that the thin, green vascular cambium layer, located just beneath the bark, aligns precisely on at least one side of the union. This layer is responsible for producing the callus tissue that will heal and fuse the two pieces into a single organism. Once aligned, the entire graft union must be wrapped tightly with a specialized material like grafting tape or a rubber band to hold the pieces immobile and exclude air and moisture.
Budding: An Alternative Method
Budding utilizes a single vegetative bud instead of a full length of scion wood. This method is advantageous because it conserves the limited supply of scion material, allowing for the propagation of many more trees from a single source. Budding is typically performed later in the season, often in late summer or early fall (July to September), when the rootstock is actively growing and the bark is easily separated from the wood, a condition known as “slipping.”
T-budding is a widely used technique where a T-shaped incision is made through the bark of the rootstock. A single bud, cut with a small piece of attached bark and wood (a bud shield), is then inserted into the pocket created by peeling back the T-cut flaps. The wound is then tightly wrapped with budding rubber or tape, leaving only the bud itself exposed, to keep the union moist and promote healing before the tree enters winter dormancy.
Post-Cloning Care and Establishment
Immediately following the grafting or budding procedure, the newly created union requires specific care to ensure successful healing and establishment. For grafts, all exposed cut surfaces, including the tip of the scion and the entire wrapped union, should be sealed with grafting wax or compound to prevent desiccation and pathogen entry. Preventing moisture loss from the scion is essential, as dry air can cause the tissue to die before the vascular systems can connect.
The newly grafted tree should be planted immediately or stored in a cool, moist environment to encourage callus formation. A crucial long-term task is the removal of any shoots or suckers that grow from the rootstock below the graft union. These shoots are genetically distinct and compete for the tree’s energy, which needs to be directed toward the scion for successful growth. Successful healing is indicated by the swelling of the graft union and the eventual breaking of the scion’s dormant buds in the spring.