Verbena bonariensis often die in winter as they're not fully hardy in the UK although in a warm sheltered position they may survive a milder winter .

They grow again very easily from seed or they take extremely easily from cuttings taken about now . You could over winter them in a frost free light position.

Here are some I did 2 years ago

http://www.flickr.com/photos/31559373@N00/4908670818/

Thankyou anchorman for such a quick reply, my plants haven't a lot of leaves on, long stalks, but |I will collect seed later in autumn, should I let the flowers go brown before I collect to dry. mags I am so pleased to find this website, it is so helpful

You do need to protect the crown from frosts and every autumn, I cover mine with a mulch of compost. I also find if they are left they self seed so look out for new ones in early summer.

I've never collected seeds . I just wait for them to self seed which they do prolifically and I pot them up into 3 inch pots when they're about 2 inches tall.

One plant can produce dozens of seedlings if the conditions are right.

Another poster was saying recently that she's thrown hundreds away this year that self seeded in the gaps between the flagstones on her patio.

I'd also recommend you take some cuttings as they start the next year bigger and more powerful and often flower better than seedlings

Find this frost thing rather strange. We are in a very frost prone area (Frost every month of the year now, except August) and over the last 2 winters the temps have been incredibly low (-23c at one point) and yet we have lost very few Verbena bonariensis. Our soil is very well drained admittedly. We have never done anything to protect the plants either.

Funny you should say that Owdboggy! as I had mine 2 winters (in heavy clay) before I knew about protecting the crowns, but I am in the South east.

I am in Essex and Bonariensis mostly seems to survive the winter here. Agree with Anchorman that seedlings are easiest to grow on. They seem to like a group planting, and grow up very rapidly from a few inches tall to blooming in our garden. Leave them where they are and mulch them as you are further north and the season can be 2-3 weeks later there when I compare my brother's garden to our garden. The survivors will guarantee you lots of flowers. The new ones not so much.

Thank to everyone who responded to my question re bonariensis I have taken all this on board and will mulch
when autumn comes I think the ground holds too much moisture for them, will try to get some gravel sand into the soil when they have finished flowering