Grafting

What is Grafting in Plants?

Also known as graftage, grafting is a technique used in farming or gardening to join at least two plant tissues so they can grow together as a single plant. Whereas the lower section of the grafted plants is known as a root stock, the upper part is referred to as a scion.

The vascular tissues of the two joined plants are expected to combine in a process known as inosculation for the grafting to become a success. Grafting is commonly practiced in gardening and horticulture to foster asexual propagation in plants grown for commercial use.

However, you can easily graft your fruit trees in your garden or backyard to gain the benefits of joining two different plants into one. The root stock or stock is selected to act as the root system of the new plant developing from the grafted plant tissues.

The scion, on the other hand, is chosen for its fruits, leaves, stems or flowers. The plant resulting from the grafted plant tissues inherits desirable genes from the scion for production in the future. Grafting is believed to have started before 2000 BC in China (according to research) and 1400 BC as evidenced in the Bible: Leviticus 19:19.

                                Plant Grafting

                                    Plant Grafting

Advantages of Grafting

Gardeners and farmers engage in grafting for many reasons. Whether you're familiar with grafting or not, here are some benefits of joining your fruit trees to grow as one plant:

  1. Eases Propagation

Crops or plants that cannot be propagated through cuttings are often grafted to facilitate propagation. It also comes in handy if growing any particular plant using other means is costly. Therefore, grafting is a cost-effective way of growing certain plants.

  1. Provides Sturdiness to Ornamental Plants

Trunks of strong and tall plants can be used as root stocks for ornamental trees and shrubs to offer them increased support and sturdiness. Ornamental trees such as weeping cherries and 'standard' roses are often grafted to provide them with sturdy support. The latter are roses propagated on high stems or root stocks.

  1. Develop Resistance to Pests & Diseases

Root stocks tolerant to certain pathogens, diseases and pests often found in soil can be used to propagate plants susceptible to them. Grafting ensures such plants grow successfully to maturity.

  1. Induces Dwarfing

Grafting can induce certain desirable attributes from the root stock to the scion. For instance, the scion of grafted plant tissues can inherit attributes such as tolerance to cold and dwarfing. High density, partially- or fully- dwarf trees are often used as root stocks of apple scion plant tissues.

  1. Develops Hybrid Plants

High breed fruit trees take at least a decade to flower and develop fruits. With grafting, the time taken by such trees to flower and develop fruits is greatly reduced. As a result, hybrid plants can mature faster and produce fruits within a shorter period.

  1. Develops Hardiness

Plants with weak root systems can be grafted on root stocks with high tolerance to difficult conditions so they can develop hardiness.

  1. Provides Pollen Grains

Grafting can also help provide pollen grains to fruits or plants with no access to pollen for flowering and fruit development.

  1. Consistency Development

Fruits can vary in size, flower and flavor, even when picked from the same tree. Therefore, grafting can help ensure that fruits develop consistently.

Precocity to reduce fruiting time in fruit trees, repair of damages or injuries on tree trunks, making scions more profitable and functional/ornamental uses in shaping trees are other benefits of grafting.

Common Types of Grafting/Grafting Methods

There are many types of grafting as follows:

  1. Whip Grafting

Whip grafting involves cutting of the root stock and the scion in a slanting way for joining. A tape is then used to bind the slanting sections of the two plants at the grafting point. Soft wax is then applied on the grafting point to prevent germ infection and keep the area hydrated.

                                    Stock & Scion for Whip Grafting

                                    A Root Stock with Scion for Whip Grafting

Although whip grafting is the most difficult type of grafting to master, it provides the largest contact surface area  between the root stock and the scion. Therefore, it has the highest success rate. Also referred to as whip and tongue graft, whip grafting is often used in commercial top-dressing of fruit trees.

The root stock and scion often range in diameter from 1cm (0.5 inches) to 1.25cm (0.375 inches). A sharp knife is used to make a slanting cut on the root stock at a shallow angle. However, if the stock is on a branch instead of a trunk, make a cut with the open surface facing outwards.

Whip Grafting

A Whip Graft

Slice the scion at the same angle, but beneath a bud. The slanting cut should face the opposite direction of the cut surface of the root stock. Next, a notch is sliced downwards into the cut surface of the root stock. A similar notch is cut upwards into the cut surface of the scion.

The notches on the root stock and the scion act as the tongues of the two plants to be grafted. With proper notch-making or cutting skills, the tongues should easily lock into each other. A tape is then bound on the joint to hold the root stock and the scion together.

Finally, grafting wax or any other compound used to seal trees is applied on the grafting surface to prevent infections brought about by germs while keeping the area hydrated. The creation of an elongated 'Z' shape on the grafting parts doesn't just eliminate the need for a companion rod, but also increases strength.

  1. Approach Grafting

Also known as inarching, approach grafting is a technique used to join at least two plants that are not easy to join. It involves growing the two or more plants close to each other to ensure that each plant to be grafted has both a root stock and a scion.

    Successful Approach Grafting

The Scion & Root Stock of Plants for Approach Grafting

Although the scion and root stock might be separated from their parent plants after grafting, they both retain them initially. Approach grafting can be successfully done at any time during the year. It is often used in pleaching.

  1. Awl Grafting

Awl grafting requires an experienced grafter to obtain the best outcome. Otherwise, a newbie gardener can easily reduce the chance of a scion surviving by accidentally driving the tool in use farther into the root stock than it should go.

                                        Awl Grafting

                                    A Successful Awl Graft

A screwdriver is often used in awl grafting to create slits at the bark of the tree for shallow penetration without getting into the cambium layer. When done, the wedged scion is inserted into the incision made earlier on the root stock to create a lock.

Moreover, this grafting technique takes the least resources and time to join at least two different plants.

  1. Four-Flap Grafting            

Also known as a banana graft, four-flap grafting was first practiced in 1975 in Oklahoma. It is often used in pecans. Despite being complex, the graft can offer maximum overlap of the cambium to get the best results.

                                Four-Flap Grafting

                                   Four-Flap Grafting

      5. Cleft Grafting

    Cleft grafting involves making small cuts into the stalk of a plant. Afterwards, the scion's pointed end is inserted into the small cut on the root stock. Although cleft grafting is most successful in spring, it is the most common type of grafting among gardeners and farmers.

    This type of grafting is perfect for joining thin scions with thicker root stocks or branches. Whereas the scion should measure 1cm in diameter, the root stock can range in diameter from 2cm to 7cm. The root stock should have 3 to 5 buds and be split right in the middle, at about 3cm deep to from a cleft.

                          Cleft Graft after Many Years

                             Cleft Grafting after a Few Years

    Cut the cleft horizontally if the root stock or branch isn't vertical. A sharp knife is used to cleanly cut the scion to a long yet shallow wedge with just one cut on each surface. Make a third cut across the wedge edges and slide it into the cleft to force the cambium layer between the wood and bark.

    What it Takes to Graft Successfully

    There are various factors you must consider to ensure your grafted plants join successfully. Consider the following:

    • Root Stock & Scion Compatibility

    Only plants with vascular cambium can be grafted because the process involves joining of the root stock and scion vascular tissues. This means monocot plants cannot be grafted. The success rate of a graft union is high in plants that are genetically related, including intra-species plants and clones with similar genetics.

    • Grafting at the Right Plant Stage

    The appropriate time to graft is when the root stock and scion are at a stage where they can produce tissues such as callus to respond to plant wounds. At this stage, the scion should be dormant to ensure the grafting site has sufficient moisture to sustain successful development of the grafting union.

    High temperatures can halt or slow the process of callus development whereas extremely warm temperature can lead to premature budding. Therefore, it's important for the temperature to be right as it can affect plant physiological stages.

    • Pressure & Alignment of the Cambium

    The root stock and scion should be oriented towards normal growth and tightly pressed at the vascular cambium. With the right pressure and alignment at the cambium where the two plants join, tissues join faster to facilitate easy flow of water and nutrients from the root stock to the scion.

    • Graft Site Care

    The graft site requires proper care after grafting over a certain period to regain good health. The site is taped then waxed to minimize loss of water and prevent infections. A string or twine can also be wound around the grafting site to offer structural support; however, this depends on the type of graft used to join the root stock and the scion.

    Tools Used for Grafting

    • Cutting Tools - Sharp and clean cutting tools such as knives are used for grafting to prevent damaging plant tissues and spread of diseases through dirt, respectively. A sharp knife with a 3-inch blade and a 4-inch handle is recommended for grafting.

                                                          Grafting Knife

                                                                      Grafting Knife

    Surgical knives, bud-grafting knives and pruning knives are special types of knives often used for grafting. Chisels, cleavers and saws are also used if the root stock is so large that a knife cannot cut through its trunk or stem.

    • Graft Seals - The need to keep the graft site hydrated goes without saying. Graft seals are tightly wound around the graft site to prevent loss of moisture, but loose enough to enable the joined plants to grow. Wax, clay, adhesive and petroleum jelly are often used as graft seals.
    • Disinfectants - Disinfectants and sterilizing agents such as absolute alcohol are used to treat the blades of cutting tools to kill pathogens at the grafting site that might cause diseases.
    • Tying Materials for Support - Nail, twine and splint strips are used in grafting herbaceous plants to add pressure on the grafting site to support and hold the root stock and scion together; this facilitates the joining of tissues from the grafted plants.

    Support materials are often damped to prevent desiccation from occurring at the grafting site.

    • Machines for Grafting - Grafting doesn't just require skills, but is also time-consuming, hence the need for grafting machines. Due to intensive and limited land use in Korea and Japan, seedling grafting is automated to save time. There are machines with the capability to graft up to 800 seedlings within an hour.

                Machine for Grafting

               Machine for Grafting in Use

    Natural Grafting

    Also known as inosculation, roots and branches of trees of the same species often graft naturally. Roots of different trees make physical contact when their barks strip off, exposing their vascular cambium to enable root grafting.

    Root grafting allows different trees to share nutrients and water to the advantage of weaker trees. It also allows regeneration as is typical of the California black oak, fosters resistance to fire and offers protection from damages caused by strong winds; root grafting enhances the mechanical stability of trees.

                                       Natural Grafting of the Blackthorn Tree

                                        Natural Grafting of the Blackthorn Tree

    Natural grafting can also occur at a point where two plant stems join; this is common in potatoes and strawberries. However, root grafting in Albino Redwoods is a type of plant parasitism on ordinary redwoods. Root grafting also allows pathogens to spread from one plant or tree to another; a good example is the Dutch elm disease.

    Herbaceous plants harbor little to no vascular cambium secondary growth and have short-lived roots, hence they rarely engage in inosculation or natural grafting.

    Graft Chimera

    This is where the root stock tissues grow into the scion in a 'graft hybrid' process, resulting in hybrid shoots as well as foliage and flowers specific to either of the two joined plants. Although results from cactus are hard to replicate, the plant can produce graft chimeras if subjected to the right conditions.

                                               Hybrid Graft Chimera

                                              Hybrid Graft Chimera

    Scientific Application of Grafting

    Virus indexing in plant viruses transmission, flowering research and genetic engineering (to transfer chloroplasts plant DNA) are major applications of grafting in scientific research.

    Herbaceous Grafting

    Vegetables and other non-woody plants can easily be grafted to take advantage of root stocks that are resistant to diseases. Grafting robots have been used in Japan for decades to reduce the time taken to graft plants. Plastic tubing doesn't just offer plant protection for faster healing at the grafting site, but also prevents desiccation.

    With proper knowledge on grafting, you can easily graft crops or plants in your indoor/outdoor garden to benefit from the many advantages of grafting. All you have to do is ensure that your grafting plants, process and aftercare activities conform to the factors that lead to successful grafting.

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