Best done in summer - there's an online tutorial on taking cuttings from verbena. Otherwise, V. bonariensis self seeds quite freely, or you can collect the seeds and sow them and grow more that way.

I've been growing them for years and never taken cuttings although I know you can. As Bamboo says, they self-seed freely (all over the place) and it's easy enough to transplant them. They grow quickly and i reckon on them lasting for two seasons providing they get through the winter. Good luck if you take cuttings but my plants are not good enough at the moment. There will be some seedlings showing in a few weeks from which I hope to continue the line.

Many thanks both. They don't seem to self seed where I am now anything like my previous place so I was going to try cuttings but I think I will also collect seeds and try and propegate from those later in the year.