Grafting and Budding Nursery Crop Plants

Introduction to Grafting and Budding

Grafting and budding are plant propagation techniques that join parts from two or more plants so they grow as a single plant. The upper part of the combined plant (scion) becomes the top of the plant, producing the branches, leaves, flowers, and fruit. The lower portion (rootstock) becomes the root system, determining plant size, hardiness, and adaptability to soil conditions.

Budding is essentially a form of grafting where only a single bud, with a small piece of bark, is transferred from one plant to another rather than a larger piece of stem.

Why Graft and Propagate Plants

Grafting and budding offer several important advantages for nursery crop production:

• Reproduction without genetic change: Grafted plants produce identical clones of the parent plant, preserving desirable characteristics.
• Improved disease resistance: Using resistant rootstocks can protect plants against soil-borne pathogens.
• Enhanced hardiness: Dwarfing rootstocks allow growers to control plant size for easier management and harvesting.
• Earlier fruit production: Grafted plants often fruit earlier than those grown from seed.
• Compatibility improvement: Some plants can be grown on rootstocks that survive under conditions where they would otherwise fail.
• Pollination benefits: Specific varieties can be combined to ensure cross-pollination.

Grafting Techniques

Whip Grafting

Whip grafting (also called tongue grafting) is commonly used when the rootstock and scion are approximately the same diameter, typically 1-2 cm. It involves making matching diagonal cuts on both pieces, with a tongue cut to provide additional surface area for cambium contact.

Steps for whip grafting include:

1. Make a smooth, diagonal cut about 2-5 cm long on both the rootstock and scion.
2. Make a second cut downward from the first cut, forming a "tongue" about one-third down from the tip on both pieces.
3. Join the pieces together, ensuring the cambium layers align perfectly.
4. Wrap securely with grafting tape or rubber banding material.
5. Apply grafting wax or sealant to prevent desiccation.

Cleft Grafting

Cleft grafting is one of the oldest and simplest methods, used when the rootstock diameter is significantly larger than the scion diameter. It's particularly useful for top-working established trees.

The process involves:

1. Preparing the rootstock by cutting it straight across with a sharp knife or saw.
2. Making a vertical split or "cleft" in the center of the cut surface.
3. Preparing scions with wedge-shaped bases.
4. Inserting scions into the cleft, ensuring cambium alignment on at least one side.
5. Sealing the entire area with grafting wax or similar material.

Bark Grafting

Bark grafting (also called rind grafting) is used when the rootstock is considerably larger than the scion wood. This technique works best when the bark is slipping (can be easily separated from the wood).

The procedure includes:

1. Cutting the rootstock straight across to create a clean surface.
2. Making a vertical slit through the bark.
3. Gently lifting the bark to create a pocket.
4. Preparing scions with a basal cut that is long and sloping.
5. Inserting scions between the bark and wood with the sloping cut against the wood.
6. Ensuring good cambium contact along one side.
7. Sealing the graft union completely.

Bridge Grafting

Bridge grafting is a repair technique used when the trunk of a tree has been damaged by rodents, machinery, or disease. The purpose is to reconnect the vascular tissues above and below the damage.

Steps include:

1. Cleaning the damaged area to expose healthy wood and bark.
2. Preparing scions (dormant wood from the same tree works best).
3. Trimming both ends of scions to long, sloping cuts.
4. Making corresponding cuts in the bark above and below the injury.
5. Inserting scions so they bridge the damaged area.
6. Securing scions with nails or grafting tape.
7. Covering the entire area completely with grafting wax or sealant.

Approach Grafting

Approach grafting involves both plants remaining with their own root systems until the graft union forms. The technique is useful when other grafting methods fail, particularly for plants that are difficult to propagate.

The process involves:

1. Positioning the two plants so parts to be joined are in close contact.
2. Making matching cuts on both surfaces to be joined.
3. Bringing the cut surfaces together and securing them firmly.
4. Wrapping the union with tape or grafting material.
5. Waiting for the union to strengthen before severing the plant that will become the scion from its original root system.

Budding Techniques

T-Budding

T-budding (also called shield budding) is the most common budding technique, performed when the bark is easily separated from the wood, typically during the growing season. This method is particularly useful for fruit trees, roses, and many ornamental plants.

The procedure consists of:

1. Selecting smooth, healthy bark on the rootstock and making a vertical cut about 2.5 cm long.
2. Making a horizontal cut at the top of the vertical cut to form a "T" shape.
3. Lifting the bark gently at the intersection of the cuts.
4. Cutting a bud from the scion with a small shield-shaped piece of bark and wood beneath it.
5. Inserting the bud shield into the "T" opening, positioning it properly.
6. Wrapping the area with budding rubber or tape, leaving the bud exposed.

Patch Budding

Patch budding is used when the bark is tough or thick, making T-budding difficult. It involves exchanging a rectangular piece of bark containing a bud from the scion with a similarly sized piece removed from the rootstock.

Steps include:

1. Using a double-bladed knife to cut two parallel horizontal cuts about the size of the bud patch.
2. Connecting the ends with a vertical cut to remove the bark patch from the rootstock.
3. Removing a matching patch containing a bud from the scion wood.
4. Placing the bud patch into the prepared area on the rootstock.
5. Wrapping securely but leaving the bud exposed.

Chip Budding

Chip budding works well when the bark is not slipping, making it a good technique for use at various times of the year. It involves removing a small chip of wood containing a bud from the scion and inserting it into a corresponding chip removed from the rootstock.

The process includes:

1. Making a shallow upward cut about 2 cm long on the rootstock.
2. Making a downward cut of the way from the base of the first cut, meeting it at a 45 angle to remove chip of bark and wood.
3. Cutting a similar chip from the scion wood with a bud in the center.
4. Placing the bud chip into the rootstock, aligning the cambium layers on at least one side.
5. Wrapping securely, leaving the bud exposed.

Rootstock Selection

Choosing the appropriate rootstock is critical for the success of grafted plants. Considerations include:

• Compatibility: The botanical relationship between scion and rootstock affects graft success. Generally, plants in the same genus graft most readily.
• Disease resistance: Some rootstocks provide resistance to soil-borne diseases and pests.
• Size control: Dwarfing, semi-dwarfing, and standard rootstocks affect the ultimate plant size.
• Hardiness: Rootstocks can improve cold hardiness or adaptability to specific climate conditions.
• Soil adaptability: Different rootstocks vary in their tolerance to soil conditions, including pH, moisture, and texture.
• Vigor: Rootstocks influence the overall growth rate and productivity of the scion.

Preparation of Scions

Proper scion collection and handling is essential for grafting success:

• Collect scions from healthy, disease-free parent plants with desirable characteristics.
• For most grafting techniques, collect dormant scions during late winter when plants are fully dormant.
• Choose straight, smooth wood of the previous season's growth, approximately - inch in diameter.
• Store scions properly to maintain dormancy until usekeep moist but not wet, in refrigerated conditions (34-40F/1-4C).
• Wrap scions in moist paper towels or sphagnum moss, place in plastic bags, and seal to prevent desiccation.
• Label all scion material with variety and collection date.
• Before grafting, rehydrate scions by soaking in water for several hours if they have been stored.

Timing and Environmental Conditions

Success in grafting and budding depends largely on proper timing:

• Dormant grafting: Most grafting of deciduous plants is performed in late winter to early spring, just before new growth begins.
• Budding: Most budding is done during the growing season when bark is slipping easily, typically late summer for many species.
• Temperature: Optimal temperatures for rapid callus formation are 68-86F (20-30C). Avoid grafting during extreme temperature periods.
• Humidity: High humidity around the graft union helps prevent desiccation of the cambium layer.
• Aftercare conditions: Grafted plants should be protected from direct sunlight and wind until the union has strengthened.

Aftercare of Grafted Plants

Proper care after grafting significantly improves success rates:

• Moisture management: Keep soil moist but not waterlogged to support healing while preventing root diseases.
• Humidity control: Maintain humidity around the graft area to prevent drying of the cambium layer, especially during the first few weeks.
• Temperature protection: Provide shade to prevent excessive heat buildup around the graft union.
• Binding maintenance: Check wraps regularly to ensure they are secure but not constricting as the plant grows.
• Competing growth removal: Remove any shoots emerging from below the graft union to direct energy to the scion.
• Gradual acclimatization: Gradually expose grafted plants to more challenging conditions as the union strengthens.
• Budding aftercare: For budded plants, after bud growth begins, remove the wrapping material carefully to prevent girdling.

Common Problems and Solutions

Understanding potential issues helps prevent graft failures:

• Poor cambium alignment: Ensure cut surfaces match precisely with cambium layers in contact on at least one side.
• Drying of the graft union: Maintain humidity and use proper sealing materials to prevent desiccation.
• Physical damage: Protect grafted plants from wind, animals, and mechanical damage during healing.
• Incompatibility: Research scion/rootstock combinations to avoid genetic incompatibility.
• Pathogen infection: Use sterile tools and clean surfaces to introduce pathogens into the graft union.
• Premature growth: Discourage new growth on the scion until the graft union has fully formed.
• Improper timing: Perform grafting during the appropriate season for both the species and technique being used.
• Overgrowth of rootstock: Remove vigorous shoots from the rootstock that would compete with the scion.