As long as the ground isn't frozen, it's actually one of the best times to plant herbaceous plants. I've been creating a new border, and have no hesitation in planting it up. Just make sure the plants are all hardy ones. Some might benefit from a mulch round the root area.

Frost is neither here nor there, as long as the potted plants have been outside all the time. As Spritzhenry says, its only if the ground is frozen (or waterlogged) that you shouldn't plant. Even when the air temperature is zero degrees C overnight, the ground doesn't freeze.

Agree with all the above comments

Planting 700 herbaceous plants next week at work. Can't wait :-)

the other option is very early spring but they should be fine as said .

Could you ask them for some kind of guarantee that they will replace any that do not survive the winter? However, it is the best time to plant hardy herbaceous as the roots can get growing even though the tops look as if they are dying back. They will need less watering next year as their root systems will be more established (remember the dry Spring this year?).

we had a very wet spring hear in norfolk .

Lol Snoopdog! At least you're honest - but now you've learned something too;-)