Advice
Grafting Ornamentals
The purpose of grafting is to combine one plant's qualities of flowering or fruiting (scion plant) with another plant, which has qualities of vigour and robustness (the rootstock). The act of grafting exposes the cambial layer (a thin regenerative layer just below the bark) of each plant and then firmly binds them together. The wound forms a callus, and the scion and rootstock bond to form the new plant.
High value ornamental trees such as Magnolia, Acer and conifers are generally container grown. Because they are grafted under cover this is known as bench grafting. Whereas fruit trees and roses are grafted onto rootstocks that are growing outdoors in the ground. This is known as field grafting.
Grafting is one of the most expensive methods of propagating ornamental plants and is usually only used:
- when plants are hard to propagate by other means, such as cuttings or do not breed true from seed.
- to strengthen plants that grow weakly on their own root systems.
- to produce a larger flowering plant in a shorter period of time.
Timing
Ornamental plants are usually grafted in early spring before the sap starts to rise but can also be done in autumn. There are many different styles of grafts but in the UK a side spliced graft is probably the most popular for ornamental trees and shrubs. Chip budding and T budding is also used.
Some commonly grafted ornamental plants are Acer palmatum, Hamamelis, Wisteria, Thuja and Picea. Most plants need to be grafted within their own species i.e. Acer palmatum cultivars onto an Acer palmatum rootstock. However, it is sometimes possible to graft within a genus i.e. A. japonicum, A. circinatum and A. shirisiwanum can all be grafted onto Acer palmatum rootstock. A few plants can be successfully grafted onto different species providing they are within the same family. For example, Fothergilla onto Parrotia rootstock, both being in the Hamamelidaceae family. For grafting pines a rough rule of thumb to remember is a five-needle pine can be grafted onto a five-needle pine, the same applies for three and two needle pines. There are always exceptions to these rules and it can be a case of trial and error.
The most important things to remember when attempting to graft a plant is to use healthy material, have a very sharp knife that is regularly sterilised and cut straight so surfaces meet flush.
Side spliced grafts
Side spliced grafts are often used for the production of ornamental trees and shrubs. Grafting is usually undertaken in late winter or early spring before bud break. Scion-wood should be from healthy one- to two-year-old wood. Cut this just above a bud into 15-25cm (6-10in) lengths. Rootstocks for ornamentals are often two-year-old seedlings, ideally about pencil thickness.
Cut the rootstock down to about 8cm (3in). Make a downward nick about 3cm (1.25in) below the top of the rootstock. Then, starting at the top of the rootstock, make a downward sloping cut to meet the first cut. Remove the slither of wood.
Take the scion-wood and make a cut along one side the same length as that on the rootstock. Make a short angled cut at the base of the scion wood. Fit the base of the scion-wood into the rootstock so that the cambiums (green layer just under the bark) meet. It is preferable if they touch on both sides of the stem but usually satisfactory if they only meet on one. The key to grafting is to make straight cuts so the rootstock and scion fit snugly.
The graft should then be wrapped with grafting tape, polythene strips or raffia and any exposed cut surfaces painted with grafting wax. If possible, place in a propagator or greenhouse. Do not overwater the compost but mist regularly. The graft if successful should start to show new growth in about six to eight weeks.