Not sure if they're hardy but I just allow mine to self seed. They will come up anywhere and I've given loads to friends. So far they've survived the winters but probably won't if it's a hard one.

As for planting out, why not do 50/50 and see how the outside ones survive?

They're fully hardy throughout the UK, and you're in the mild South West, so they'll be absolutely fine outside.

Sorry, Rosierose, they are not fully hardy throughout the UK - they can and do bite the dust in even a chilly winter, never mind bitter cold one. Usually, though, seed has dropped in the area and new plants start growing all over in spring...

In a sheltered spot, mature plants will get through an average winter, albeit looking a bit ravaged - but the young ones, not so much. However, MerlinBd - you're in Devon, so if you're planting somewhere sheltered, provided we don't have a humdinger of a winter (and we might, this year) they should come through. I'd do 50/50 as suggested by Arbuthnot...

Odd, they have come through the extremely bad winters of a few years back, here, as mature plants and seedlings. Spend as much time weeding these out as any plant.

Thankyou all. I'll do 50/50 as Arbuthnot suggests. Things don't seed too easily in my garden apart from Welsh Poppy and Geranium Oxanium so I'm pleased that these have done better this year, mainly between concrete flags..
Perhaps the dampness is a deterrent?

Not sure, Merlinbd... I just notice that some years there are loads and loads of seedlings, other years very few. Probably to do with temperature and moisture levels in early to mid spring... if its too dry, they won't germinate either. They certainly seem to like lighter soil conditions, I get loads germinating in cracks in paving and in pots and tubs...

Owdboggy - I lost all these in different gardens here in London back in 2010 when we had the bad winter, when loads of Cordylines got killed - luckily, plenty of seedlings arrived instead. Hardy down to -5 deg C I think...so -12 would have been too much for them for sure that year.

As I said, odd. They survived here the year it went down to -24c (-8c in the greenhouse, under the bubble plastic covering) and no snow cover either. We have never replanted them in the last 20 years.

@Bamboo - I speak from personal experience, as I've never lost any V.b seedlings, even when temps plummeted to -10 a few years ago (and they were in open ground). Plus, if you check the RHS website, you'll see they too say they're fully hardy throughout the UK, let alone in milder regions such as Devon which is where the OP lives.

Owdboggy - were yours in the greenhouse or outdoors? Seems odd yours survive outside and ours don't - you're not near the coast, are you?

We are about as far from the coast as one can get and in a real frost pocket. The plants are spread out all over the garden, where they choose to grow really.

Very odd - I'm just wondering whether dryness at the root in autumn might be the cause, rather than the cold... its entirely possible, most of my customers never did keep up with the watering...

I have never managed to keep them in my borders overwinter, think it was a mix of too dry and baked hard soil. Tried a couple of times because I do like them but have given up on them now.

Oh hecK! so much conflicting info! I'll keep trying. But such an interesting discussion. Ta very much.