Plant grafting is a precise horticultural technique that joins two separate plant parts so they grow together as a single, functional organism. This process involves physically connecting the stem tissue of one plant, known as the scion, onto the root system or stem of another, called the rootstock. When successful, the vascular systems of the two components merge, allowing water and nutrients to flow between them. This article covers the essential preparation, the cutting techniques, and the subsequent aftercare required for a successful union.
Why Grafting is Necessary
Grafting allows growers to combine the desirable characteristics of two different plants into one specimen. This practice is often used to confer disease or pest resistance from a hardy rootstock to a susceptible scion. For instance, a flavorful fruit variety can be grafted onto a rootstock resistant to common soil-borne pathogens, ensuring the scion’s survival and productivity.
The technique is also used to control the size and growth habit of trees, particularly in commercial orchards. Grafting a scion onto a dwarfing rootstock results in a significantly smaller tree that bears fruit earlier than it would on its own roots. This speeds up the time it takes for a plant to mature and produce a harvest.
Grafting is the most common method for propagating certain cultivars, like many fruit trees and ornamental roses. This is necessary because their cuttings do not root reliably or their seeds do not produce plants true to the parent type.
Essential Preparation and Timing
Successful grafting requires the selection of appropriate plant material and correct timing. The scion, the young shoot from the plant you wish to propagate, must be collected while the plant is fully dormant, typically in late winter before the buds begin to swell. Ideally, the scion wood should be one-year-old growth, about the thickness of a pencil. It must be kept moist and refrigerated until grafting to maintain its dormancy.
The rootstock provides the root system and is selected for traits like hardiness, soil tolerance, or dwarfing characteristics. Grafting is generally performed in early spring, just as the rootstock is beginning to break dormancy and the sap is starting to flow. A sharp, specialized grafting knife and securing materials like grafting tape or budding rubbers are necessary to ensure clean cuts and a tight fit.
Step-by-Step Grafting Techniques
The fundamental principle in any grafting technique is the precise alignment of the cambium layers of the scion and the rootstock. The cambium is the thin layer of actively dividing cells located just beneath the bark, and its proper contact is the biological requirement for the two parts to fuse. The Whip-and-Tongue graft is a popular technique for joining scions and rootstocks of similar diameter, offering mechanical stability through an interlocking cut.
To perform this graft, make a long, smooth, sloping cut, about one to two inches long, on the bottom of the scion and the top of the rootstock. A single, clean slice is preferable to minimize tissue damage. Next, cut a downward “tongue” into the face of the first cut on both pieces, starting about one-third of the way down the slope. These cuts should be made carefully to avoid splitting the wood.
The scion and rootstock are then immediately pushed together so the interlocking tongues hold them securely, maximizing the surface area contact between the cambium layers. If the diameters are not perfectly matched, align the cambium on at least one side of the graft union. The Cleft Graft is used when the rootstock is significantly larger than the scion. In this case, a wedge-shaped scion is inserted into a split made in the top of the larger rootstock, ensuring the cambium layers meet.
Post-Grafting Care for Successful Union
Once the scion is secured to the rootstock, the union must be wrapped tightly with specialized grafting tape or budding rubbers. This holds the pieces immobile and compresses the cambium layers, promoting the formation of callus tissue. Callus tissue consists of undifferentiated cells that bridge the wound. All exposed cut surfaces, including the tip of the scion, must be completely sealed with grafting wax or a similar compound. This sealing prevents the tissue from drying out and protects against invading pathogens.
Newly grafted plants should be placed in a protected environment, such as partial shade, to reduce moisture loss and stress on the scion. Monitoring involves regularly checking for signs of desiccation, indicated by shriveling of the scion wood.
Any new shoots emerging from the rootstock below the graft union, often called suckers, must be removed immediately. This ensures the plant’s energy is directed toward the scion and the healing process. The securing materials should remain in place until the union is visibly healed and the scion shows robust new growth, a process which can take several months.