Why Do Roses Produce Suckers?
It's not uncommon for rose plants to be grafted onto hardier root stocks. Grafting means joining two plants together to gain some benefit. With roses, the benefit is hardiness and health. Many roses are grafted onto the rootstock of a hardier rose. The top part of the plant, the scion, is the rose variety you are purchasing. This is the part that blooms and it will produce the rose flowers you are expecting. However once grafted, its roots can handle colder winters and may gain some disease resistance as well. This helps the rose bush survive in colder climates.
In areas with harsh winters, the graft union is planted just below the soil surface. In mild climates, it can remain above ground.The graft or bud union looks like a small, knobby knot. The top cane may also go off at a weird angle from the knot.
Ideally, the root stock will send down roots and the top portion of the grafted plant will produce the canes and blooms, however sometimes things don't work out ideally. There is a chance that canes can be produced by the rootstock. These canes are called suckers, for reasons outlined below.
What is a Rose Sucker?
Suckers are canes that emerge from below the bud union, where the rose bush was grafted onto the root stock. Canes that grow out of the rootstock will not produce the rose flowers you are expecting. What they will do is "suck" the nutrients from the top portion of the rose, the part you purchased the plant for and which will produce the rose flowers you are hoping to see. That's why rootstock canes are appropriately called "suckers".
The only sure sign that a branch is a sucker and not simply new growth is that it is coming from below the bud union, although most suckers will have leaves that don't exactly resemble those on the upper portion of the rose bush. However, you can usually recognize these rouge canes by how vigorously they grow. Even if you don't recognize these suckers from their rampant growth, you will have yet another signal. Either they won't produce any flower buds at all or, if they do, the flowers will not be the color, or shape, or size you would expect from the variety of rose you bought.
How to Remove Rose Suckers
Suckers need to be removed from rose bushes or they will eventually take over the plant. Cutting suckers with pruners just seems to encourage more suckers. If you simply snip them off at the soil level, they will re-sprout and probably produce even more canes. Instead, it is recommended that you dig down to where the sucker is originating and pull, twist or tear it off. That means following them all the way down to the rootstock, which might be underground. Of course, do this as gently as possible, so that you don't further damage the plant and wear thick, protective gloves while doing this.
Don't be surprised is suckers pop up several feet from the originating rose bush. Just follow the same procedure; trace the can back to where it originates on the rootstock and tear it off.
The good news is that many newer roses are grown from cuttings, not grafts. They grow on their own root stock, so they cannot produce suckers.