verbena bonariensis - do I cut back after flowering?

This plant is a perennial in most parts of this country. They will grow each year, starting in Spring, will produce their growth/flowers over Spring Summer and Autumn and will die back over Winter and hibernate ready for Spring the next year. I tried to grow Verbena in Nottingham and didn't have any luck so I treated it as an annual there which means it will grow, flower and die all in one season.
If your Verbena is an established plant and has been in your garden growing over a few years then you should be ok. You would generally cut down the dead growth in Autumn or early Spring and the new growth will appear from the bottom of the plant at soil level. You may want to dig one of your plants up to see if it producing any new growth, give them a feed and a nice mulch of compost and you may find they will repay you with a lovely display.

It also self seeds prolifically so look for it while weeding,

Thanks for your replies, Andrearichter - think it may have gone to sleep permanently - no signs at all of life, but we are in Lincolnshire and we have had some very hard frosts this winter so think maybe I shall have to replace it. It was a new plant last season and did flower well but obviously after the very hard winter we have had it has taken its toll on my verbena. Will try again though because I liked this plant very much. thanks again for your prompt replies.

I bought one from Homebase last week - they were on offer, two for £5, along with various other herbaceous perennials in 1L pots.

I find they are short lived 3/4 yrs but self sown ones come up regularly.

I find this a strange plant. It doesn't like where I plant it but seeds and comes up elsewhere. In fact it prefers to grow between the bricks in the drive. I just leave it to do as it likes!