Datura Pruning

Hi All
I bought a barerooted Datura earlier on in the year, I planted it up in a container & it has grown away nicely, its around 12/15in tall now but it has not flowered this year probably because its still quite small, on the instructions it said to prune back hard after flowering but as its not flowered Do I still do it? if so how hard? although I do have a greenhouse I've only got this plant to overwinter so it seem a bit of a waste heating it for that so I intend on bringing it in to the extension which has a polycarbonate roof, it stays fairly cool in there even when the heating is on, or would I be better putting it in the greenhouse & wrapping it up with fleece?
Helen

 

Helen
If you put it in the extension it will keep growing and may even flower.
Nik