Occasionally the understock will produce a cane from beneath the bud union that pops up out of the ground and grows like mad. And because it is produced from below the bud union it “sucks” the nutrients up before they can get to the rose variety you purchased. Hence the term “sucker”. Eventually they will kill the rose variety you purchased and you are left with nothing but understock.
Key Takeaways:
- A grafted rose bush consists of the above ground rose bush you desire and the below ground rootstock.
- The above ground portion is typically not hardy enough to survive in all climatic conditions.
- Thus, it is grafted (budded) onto another rose that is extremely hardy so that the overall rose bush is capable of surviving in most climates.
“A grafted rose bush consists of the above ground rose bush you desire and the below ground rootstock.”
http://www.gardeningknowhow.com/ornamental/flowers/roses/removing-rose-suckers.htm