Posted: 21/12/2014 at 12:01
You can probably tell if you have suckers from the rootstock by looking for 2 subtle differences in the suckers from the main stems. They will probably be different in colour, one being a darker green, when new. The other is the number of thorns, usually more to the inch on the suckers. If you can see such differences you probably have suckers. These should be the ones growing from lower down and need to be pulled/ripped off, not cut. Cutting will encourage more, which will gradually weaken your lovely plant.
I would do this sooner rather than later, and before the Spring growth starts. Take it up now in a mild spell, and treat it like a bare root plant. Tear off the suckers, pulling downwards, and replant. Prune the whole shrub quite hard, to get a better balance between top growth and roots and away you go.