Woody plant species have self-grafted in the wild for millennia in a natural but slow evolutionary process. Ancient humans copied the natural process and produced plants that combined desirable traits while eliminating undesirable ones. Manual grafting accelerated the process of plant evolution. Grafting increases plant propagation success, creates cultivars with improved traits, hastens flowering and fruiting, develops unusual plant patterns and controls size, disease and pest resistance, according to Cornell University.
Ancient gardeners knew trees and shrubs growing close together could penetrate the bark between them and become one plant, but when and where humans began grafting is lost in time. References in the Bible and other sources are unclear, but human grafting may be as old as the second millennium BCE. Grafting temperate fruits allowed them to spread from Asia to Europe in the first millennium.
Olives were among the first plants domesticated and improved by grafting. The Apostle Paul mentioned combining good olives with wild olives in the Bible. Grafting came into its own during the Renaissance, when explorers brought exotic plants back from foreign travels. These plants were predominantly tropical but could survive European climates if grafted to hardier rootstock.
Science of Grafting
The biology of grafting blossomed in the 1700s. Gardeners joined the rootstock, the lower part of the plant that becomes the root system and stem base, to the scion, a small shoot from a separate plant with one or two buds which becomes the visible part of the new plant. Successfully joined, they create a new species. When gardeners learned to align the cambrium cells of the stock and the scion so they were in contact, grafts became more successful.
Grafting allows gardeners to reproduce plants that do not grow well from cuttings or other propagation techniques. Plants with desirable characteristics but weak or disease-prone root systems can be grown by grafting them onto hardy, disease-resistant rootstock.
Plants cross-pollinate and single new varieties sprout among their cousins. Humans graft the most promising of these because many more plants can be grown on rootstock than by planting cuttings. Hundreds of new varieties have been developed this way, speeding up natural evolution.
More than 100 grafting techniques that were developed in the 1800s are standard procedure in the 21st.
Grafts between a single species are the most successful. Crossing two species is possible. Grafting genera within a family is rare and crossing families is highly unlikely, although roses, citrus and cacti are compatible even between families.
Nurseries and research stations continue to graft plants to improve plant characteristics such as hardiness, juiciness, color and length of bloom and to eliminate undesirable ones such as those with short fruiting seasons or flowers that stay on the plant instead of dropping off.