Plant grafting is a horticultural technique that involves joining parts of two plants so they grow as a single, combined plant. This method of asexual propagation creates a unified organism by attaching a section from one plant, typically a shoot or twig, to the root system and lower stem of another.
Why Graft Plants?
Gardeners and horticulturists use grafting for several practical reasons, leveraging the strengths of different plant varieties.
- Increasing disease resistance: A hardy rootstock can provide resilience against soil-borne pathogens or pests.
- Accelerating fruit production: A young scion can bear fruit much sooner when joined to a mature rootstock.
- Controlling plant size: Creating dwarf fruit trees that are easier to manage and harvest.
- Adapting to different soil conditions: Selecting rootstocks tolerant to issues like waterlogging or poor soil aeration.
- Repairing damaged trees: Grafting new sections onto healthy underlying tissue.
- Propagating difficult plants: A reliable method for plants hard to root from cuttings or those that do not grow true to type from seeds.
How Plant Grafting Works
The fundamental principle behind successful plant grafting relies on the precise alignment and fusion of specific plant tissues. Grafting involves two main components: the “scion,” the upper part chosen for its desirable attributes like fruit, flowers, or foliage, and the “rootstock,” the lower part that provides the root system and often contributes vigor or disease resistance.
For a successful union, the vascular cambium layers of both the scion and the rootstock must be brought into close contact. The cambium is a thin layer of actively dividing cells located just beneath the bark, responsible for producing new xylem and phloem cells that transport water and nutrients. When these cambial layers are aligned, they form undifferentiated callus tissue, which then differentiates into new vascular connections, allowing the two plant parts to grow together as one integrated system.
Common Grafting Techniques
Several grafting methods are commonly employed, each suited for different plant types and objectives.
Whip and tongue grafting is frequently used for scions and rootstocks of similar, smaller diameters, typically around 1 cm (3/8 inch). This method involves making a long, sloping cut on both components, with an additional small “tongue” cut that interlocks the two pieces, providing a larger contact area for the cambium and a stronger initial union.
Cleft grafting is often used when the rootstock is larger in diameter than the scion. A split or “cleft” is made into the rootstock, and one or more wedge-shaped scions are inserted into the opening, ensuring their cambium layers align with the rootstock’s cambium.
Budding, a variation of grafting, uses a single bud as the scion rather than a larger shoot. A small section of bark with a bud is inserted into a cut in the rootstock’s stem. Once healed, the rootstock’s top portion is removed, encouraging the bud to grow.
Caring for Grafted Plants
Successful establishment of newly grafted plants requires proper aftercare. Immediately after grafting, protect the graft union from drying out by wrapping it with grafting tape, wax, or parafilm. This wrapping helps maintain humidity and provides structural support, remaining in place until new growth indicates a strong union has formed.
Newly grafted plants should be kept well-watered to support their recovery and growth. They may also benefit from being placed in a sheltered location, away from strong winds or intense sunlight, to prevent stress.
Regularly remove any shoots or suckers that emerge from the rootstock below the graft union. These shoots, genetically from the rootstock, compete with the desired scion for resources and should be pruned promptly to direct the plant’s energy towards the grafted portion.