Hazel

I have three old Hazel stumps from an old hedge that I wish to kill off. I have to keep clipping them back throughout the year and I am getting lots of new growth from the base. Any advice on how to finish them off would be much appreciated. I won't be able to dig the out as they are in a border with lots of plants around.

 

I normally drill holes and pour neat SBK into them, plug the holes with something like putty just to stop wildlife getting in contact, but unlikely.

 

I think SBK recommend doing it in autumn/winter

 

I've found when using SBK that it often works better when the plant is in growth, although autumn/winter is the recommended time, as @CarolineL states.
I've used it for blackthorn stumps, and that worked far better than using it when they were dormant. I can't say if it would be suitable for hazel, but if you still have the problem in spring, it's worth trying it again then.