Definitions for "Bud union"
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 swollen part of the stem where the scion of a grafted rose meets the under stock
The area where the bud eye was grafted on the root stock.