By Pdb
Lancashire,
United Kingdom 
I have delphinuim, verbena bonisaria, echinacea growing in my greenhouse. Will they die back naturally like they do in the garden and then grow back in spring. I have grown them from starting them in late summer early autumn.
6 Dec, 2011
Answers
It all depends on the temperature in the greenhouse throughout the whole winter. If they stay green, that's OK, and if they die down, reduce watering and they will resprout in spring. It helps to keep young plants protected over their first winter. I have found this especially true of Echinacea on my clay soil.
6 Dec, 2011
Agree with dgw - although these are classified as hardy perrenials, they should have been planted out earlier in the autumn. Keep them as dgw and volunteer says over the winter, then plant out when the soil is soft and frost free. They may not flower first year out of the greenhouse - but the weather and plants constantly surprise!
6 Dec, 2011
The delphinium and echinacea should come through ok(i would keep them on the dry side) but very young plants are never as hardy and would have been better started earlier in the year.The verbena will take very little frost and are best treated as annuals up here in Scotland.
6 Dec, 2011