Grafting is a horticultural technique used to vegetatively join the top of one plant to the base of another to the type of fruit we’re wanting but on a smaller tree.
On grafted dwarf fruit trees, the top of the plant — called the scion — produces the desired fruit variety.
It is grafted onto the base — called the rootstock — which bestows its dwarfing characteristics to the scion.
Smaller trees usually lead to earlier tree maturity and fruit production. The reduced tree size also makes pruning, harvesting and pest management easier.
It may come as a surprise to many gardeners that a number of different ornamental trees and shrubs are also grafted. There are several reasons why ornamental plants may be grafted.
▪ Rooted cuttings from cultivated varieties of ornamental plants make production of new plants exactly like the parent easy, but cuttings from some plants can be very difficult or slow to root. For example, Japanese maple cuttings are either extremely slow to root or will not root at all.
▪ Some ornamental plants have weak root systems and poor plant vigor. By grafting a desirable scion onto a more robust compatible rootstock, producers can obtain a vigorous plant more quickly and at a lower cost than if it was grown on its own roots. Until recent years, almost all hybrid roses were grafted onto a rootstock for this reason.
▪ Specialty grafting can produce plants with interesting or novel forms. A common example of this are weeping flowering cherry trees. Many of these sold to home gardeners are created by grafting a weeping Higan cherry tree (Prunus subhirtella var. pendula) onto the trunk of an upright standard cherry tree at a height of four to six feet. If grown on its own roots, the weeping Higan cherry would develop into an elegant 20- to 40-feet tall and 15- to 25-feet wide weeping tree most suitable for a large-scale landscape.
While helpful in producing ornamental plants, there can be problems with grafting. One common problem on grafted ornamental trees is the development of upright suckers from below the graft.
Ornamental Trees & Shrubs That May be Grafted
Arborvitae, ash, beech, birch, catalpa, cedar (Cedrus), clematis, cotoneaseter, dogwood, fir, flowering pear, golden chain, hawthorn, hibiscus, holly, hornbeam, horsechestnut, thornless honeylocust, mountain ash, pine, red maple, Japanese maple, oak, rhododendron, rose, sugar maple, spruce, redbud, upright junipers, viburnum, weeping pussy willow, and witch hazel.
These suckers have the characteristics, including the growth habit, flowers, and fruit of the rootstock instead of the desired scion. If suckers from below the graft are allowed to develop on a weeping cherry tree, they will have upright growth and ruin the graceful pendulous form of the tree. These suckers will eventually produce flowers and fruit that must be sprayed to control cherry fruit flies.
On non-weeping forms of grafted ornamental trees, the graft is typically close to the base of the tree. It is a swollen or slightly bulging area.
Suckers may arise beneath the graft on these types of trees too. All suckers that develop below the graft on grafted trees should be pruned off as soon as they appear, removing them as close to their source as possible.
Sometimes a graft may fail due to a poorly formed graft union, incompatibility between the scion and rootstock, or a disease infection. A scion may also suffer cold temperature injury during the winter. Graft failure or injury to the scion can lead to the death of the entire plant or just the scion. If the rootstock remains alive and is allowed to grow, it is usually a much less desirable plant and should be removed.
Now is a good time to look for and remove suckers on your grafted trees and shrubs. Check out weeping cherry trees and remove any straight upright growth coming from below the graft.
Marianne C. Ophardt is a retired horticulturist for Washington State University Benton County Extension.