The swollen area at the top of the shank from which new canes (basal breaks) emerge. In climates with extreme heat or cold, it is best to protect the bud union by planting it below the soil level and mulching over the top.
the point where the rootstock is grafted to the flowering variety. The bud union can be seen as an enlarged area at the base of the plant, whether purchased as bareroot or in a container. The bud union is also used as a gauge to mark planting depth.