I had Valerian self seed in the garden; it took about 3 years of pulling up every seedling to get rid of it; it even grows in gravel. The good thing is that it is easy to identify a young plant and just whisk it out.
Agree. Very pretty. Just pull up the bits you dont want.
It really depends if you like it or not. I allow the dark reddish pink one like this to grow at the front of the garden over a a low bit of wall, where it does look nice. All pale pink and white ones are ruthlessly pulled up, as are those which appear elsewhere. It is one of those cases where one persons weed is anothers joy and delight!
i agree it is lovely growing and tumbling down a wall, it always reminds me of the coast! just cut back when flowers fade and it keeps on flowering.