Some years ago i planted some alstemeria along by a hedge. While my wife loves the blooms and is slow to allow me exercise control over spread I feel time has come for action as they are all over the place and extremely tall. T to make matters worse some dogs seem to love to roll over in the clumps thereby knocking them to the ground. Apart from putting them in pots what is my best course of action. I am thinking of digging a trench along by the hedge in the hope it will stop spread but any ideas of how to stop them growing too tall. In a jocose way they remind me of the japanese knotweed!!