Updated: March 24, 2021
graft failure on cherry
A cherry tree showing growth of both the scion and rootstock from below the graft union. Photo: Ashley Kulhanek, OSU Extension

What is graft failure and what are the causes?

  • Grafting is a method of propagation that joins a scion (upper portion) and rootstock (lower portion) of two similar species of plants.
  • Graft incompatibility, improper technique, or environmental conditions, may cause graft failure.
  • Graft incompatibility is not clearly understood but may be the result of genetic differences between the grafted parts.
  • Abnormalities may develop in the vascular tissue at the graft union.
  • Disease-causing organisms such as viruses or phytoplasmas are other possible causes of incompatibility.
  • Care should be taken to use disease-free plant material when grafting.
tree graft failure

Graft failure. Photo: R. Heflebower

Symptoms 

  • The most pronounced symptom of graft failure is a smooth, clean breaking off of a tree at the graft union. This may occur one, two, or many years after the graft is made.
  • Other symptoms of graft failure include general ill health of the tree or shoot dieback.
  • Foliage may yellow in late summer, followed by the early leaf drop.
  • Vegetative growth of scion (part of the graft that produces growth) and rootstock may begin or end at different times. There is often a distinct difference in growth rate between scion and rootstock.
  • Overgrowth may occur above, at, or below the graft union, and results in a visible difference in the trunk diameters. Suckers can develop from the rootstock.
  • While it is possible for trees to survive with one or more of these symptoms, a combination of many symptoms may result in the premature death of the tree.
  • Weakened trees may have to be removed.

Normal bulging at the graft union

  • A slight bulging, swelling, or "crook " in a tree trunk, two to three inches above the soil line, is the result of normal healing at the graft union.
  • The site where the scion and rootstock meet is called the graft union.
  • Swelling occurs as callus tissue (tissue that forms around a "tree wound") is formed and new vascular cambium tissue develops in the callus bridge area.
  • The graft union should remain above the soil line to prevent the scion from developing roots, losing the influence of the rootstock.
normal graft union

Normal graft union. Photo: University of Maryland

Grafts and tree production

  • Nurserymen frequently use grafting as an excellent way to propagate plants not easily grown from seed or cuttings, especially the cultivated varieties.
  • It allows the grower to produce a saleable plant more quickly.
  • It also allows nurserymen to select and control desirable plant characteristics such as growth habit, growth rate, size, hardiness, and time required for fruit production.

Rev. 2020