With great difficulty, we have been trying for 14 years.

Agree with Owdboggy's comment - only thing I found that worked was paying a very strong young man to come in with a pickaxe, a fork and a spade, who spent half a day getting it all out.

Tried that, it grew back. Now I cut it back to the roots every year and spray the new leaves with Roundup. Does not kill it but the growth is reduced for a while. Our problem is that it is in the land outside our garden and creeps back in every year.