How Does Tree Grafting Work?
In nature, trees reproduce by pollination, but nursery cultivators can propagate a tree by graft to select for particular characteristics that might otherwise get lost in the natural reproductive process. In this article, we’ll examine why grafting can be so important for trees in urban, neighborhood, and orchard settings, including which tree species are most frequently propagated by grafting. Awareness of grafted tree varieties can help residents make informed choices when planting trees in the Nashville landscape!
Why Are Some Trees Grafted?
A cut branch of one tree can be grafted onto rootstock to create another plant specimen in order to conserve particular features of the parent, such as:
Fruit productivity
Appearance and size
Hardiness and environmental tolerances
Fruiting Trees
Fruiting species were the first trees to be grafted—an age-old practice that conserves the traits of the fruit produced. Most fruit trees, such as apple, plum, peach, persimmon, and citrus, make seeds that are not genetic matches of the parent tree due to cross-pollination and genetic recombination. This means that those seeds will grow into trees that produce a different variety of fruit, which might not be as tasty or sizable as the parent fruit. Grafting is a very important economic practice because it allows growers to maintain a fruit variety that will reliably bear the same type of fruit that customers will buy and enjoy.
On the other hand, some trees are grafted so that they won’t grow fruit. Some ornamental tree species, such as fruitless cherry trees and fruitless apple trees, are planted in gardens for their flowers and foliage without the messy fruit production. Ginkgo trees can be grafted to ensure that the tree is male, which won’t grow the tree’s pungent fruit. Since ginkgo trees are very hardy urban trees, they are often planted along sidewalks and roadways, where fruit droppage can result in unpleasant messiness on the hard surfaces.
Tree Size and Color
Grafting also allows the conservation of traits such as size and color, which can be important for a range of trees. Small varieties of usually large trees can allow for the presence of a species where it might not have fit otherwise, contributing to the vertical coverage of a local canopy. Dwarf varieties of a tree, such as Japanese maple, dogwood, magnolia, and redbud, are popular ornamental trees that offer a special, delicate version of their larger relatives. Fruiting trees are also cultivated in dwarf varieties for compact size and easier access to the fruit.
Other tree varieties are propagated by grafting in order to conserve their visual interest. Maple, cherry, and ginkgo are just a few of the many tree species that come in varieties that are particularly showy with their flowering in spring or their foliage in fall. Vibrance, color, and flowers are all variables considered when cultivating visually interesting trees.
Environmental Hardiness
Whether picked for ornamental or fruiting (or fruitless) characteristics, planting trees contributes to the local canopy ecosystem by providing ecosystem services like soil stability, air filtration, and wildlife habitat. Some grafted tree varieties are chosen specifically for their hardiness and performance, including shade trees like maple, London plane, linden, and honey locust. Elm is one of many tree species that have graft-bred varieties with improved resistance to diseases, pests, and urban environmental stressors like heat, cold, and compacted soil.
How Does a Tree Graft Work?
Tree grafting involves connecting the cutting of a tree to the rootstock of another specimen.
The “scion” is the branch cutting from a tree that has been selected for its traits. The bottom of the branch is cut in a way that it can be inserted into a wedge in the rootstock so that they fit together tightly.
The species of rootstock is sometimes of the same species as the scion or other times of a related type of tree. Rootstock can be chosen for tolerance to soil conditions to help the tree survive and thrive in various types of ground.
Grafting is usually done in early spring before a tree comes out of dormancy. When the scion is inserted into the rootstock, it’s wrapped with grafting tape, which keeps moisture in and pests and pathogens out of the wound and binds the fit together. In this arrangement, the inner wood of each part is in contact. They fuse as the wound-like connection heals, and the shoot and the root are then able to exchange moisture, nutrients, and hormones to manage the growth of the specimen.
Not every tree can be grafted successfully; the shoot and root have to be compatible enough in wood tissue, growth pattern, and hormones to fuse and grow as a single tree. When done correctly, grafting usually works neatly, but occasionally there can be other kinds of graft incompatibility. The rootstock may outgrow the grafted top, the scion might outgrow the rootstock, and once in a while, they just don’t join for unknown reasons. Some trees (like apples and citrus) graft very well onto a variety of rootstocks, while others (like oaks and most conifers) are much more difficult or nearly impossible to graft and are cultivated by seed.
Plant Hardy Tree Varieties in Nashville
Grafted cultivars of trees contribute to the vibrancy and resilience of Nashville’s environment, whether in their beauty, niche fit, or resilience. Often, these variables overlap with the right tree for the right place! Browse the Nashville Tree Conservation Corps’ tree sale for the newest addition(s) to your yard and choose from the hardiest cultivars of the variety of tree species available.
Consider volunteering with us, donating a tree, or making a financial contribution to support our work. As a nonprofit, NTCC relies in part on the goodwill of residents and businesses to fund our mission to promote, preserve, protect, and plant Nashville’s tree canopy! Stay informed on local tree happenings by signing up for our newsletter and connecting with us in other ways through our Linktree.