West Sussex,
United Kingdom 
Verbena bonariensis.
I have a very large potful of these self-sown from an overhanging plant. They are very healthy and strong looking and are about 6-8 ins tall. I would like to transplant them to the border. Should I do this in autumn or would it be better to wait until spring, please? They have enough room to grow on in situ for now if that would be the best thing.
11 Sep, 2012
Answers
i have a similar pot and i intend to keep them in the cold frame until spring as i have lost some in the really bad winters.
12 Sep, 2012
My previous Bonariensis seedlings all survived in our garden in Essex over the last winter and the seedlings that bobbed up this year have been either pulled up and composted or a few potted, currently out in the garden, and in bloom. I planted them in groups of six, as I think they like company. They do not like Essex dryness.
12 Sep, 2012
Thank you for these replies. I do have self seeded ones popping up most years here in the south, often through cracks in the concrete and most of them survive, but I have not had them self sown in a pot before. I need to move them at some point but I don't want to lose them and wondered whether they'd survive the winter if I did it now. I will plant some out now in a sunny spot, put some in the cold frame and keep the rest in the pot in the utility room until spring. I find they are a magnet for bees and butterflies!
12 Sep, 2012
Yes. Verbena BVonariensis is one of my favourite plants for the back of the border ,it has such a long flowering season and ,as you say the bees/butterflies love it.
I find it looks really well with this rudbeckia as the colours contrast so well
http://www.flickr.com/photos/31559373@N00/219907356/
12 Sep, 2012
In mid season I collect the self-sown seedlings and pot them up, each into 9cm pots then into 1 litre pots, cutting them back several times to make them bushey. Over-wintering them in a cold greenhouse and planting them out the next spring. I use the new plants to replace the old ones which become too woodly after a few years.
13 Sep, 2012
Many verbena bonariensis die due to cold and wet over winter in many british gardens. I have several customers with VB and some seem to survive winters well and others die.(THE VB not the customers! )
I guess it depends on the their exact position or soil type.
I'd be tempted to plant some out now and keep some in a protected environment until late spring next year, such as a well lit frost free window sill.
I'm growing about 40 VB cuttings on my small plant nursery and intend to overwinter them all indoors in an unheated bedroom on a sunny window sill. Last year I tried then in an unheated coldframe outdoors and they all died.
11 Sep, 2012