Many ornamental trees, shrubs, roses and climbing plants and most fruit trees are grafted or budded onto a rootstock of a compatible species. This is done for plants that are difficult to propagate from cuttings, where the rootstock is needed to control the rate of its growth or it imparts disease resistance.
Sometimes the graft union, where the cultivated variety (called the scion) and the rootstock are joined, can fail – sometimes up to several years after planting. The failure can be total or partial, with the rootstock and scion becoming partly or fully separated. This leads to the grafted variety breaking off the rootstock or, because it prevents the flow of water and nutrients from the roots, it dying back, poor growth or even death of the grafted variety. The rootstock, on the other hand, usually remains alive and sends up numerous suckers.
There are several possible reasons for graft failure.
Poor formation of the graft union during the propagation stage, such as: using an incompatible rootstock species or an excessively vigorous rootstock; not lining up the scion and rootstock correctly; adverse weather conditions; and poor hygiene and growing conditions.
The graft union drying out.
Physical damage to the graft union.
Poor growth and dieback shouldn’t always be blamed on graft failure, as there are numerous environmental and cultural reasons why plants don’t grow well – from poor soil preparation at planting time, waterlogging, drought, wind damage, cold temperatures and frost among others.