Overwintering Datura/Brugmansia (Angels Trumpet)

[Pandora]

I have four potted woody-stemmed Daturas I grew from seed last year that
I'd very much like to keep alive.  They spent last winter on a sun porch
where they stayed leafy but hosted spider mites.  They're too big for the
sun porch now.  I read (but can't remember where) that they go dormant
during the cold season but are only half-hardy.  Does anyone know how to
get them to go to sleep and if they could then be stored in the dark in my
root cellar (where I overwinter my potted fig) until spring?  I live in
zone 6. 
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pandora at windo.missouri.org