Maine et Loire, France

Why have my Melianthus Majors died?
I grew three good plants from seed last summer. I took the advice from someone on this site not to plant them out as they would be killed in their first winter. So I kept them in pots in the polytunnel. The foliage lasted until January, I think, and then it died back.
I've been expecting them to resprout from the pots, but they look as dead as a doornail. What did I probably do wrong? How do you keep them alive during winter when young?

On plant Melianthus

• 2 Jun, 2010