I think they window boxes look nice with some pine and holly branchs in them.

carey

I usually "plant" plastic pointsettias along with red twig dogwood and curly willow branches.

Probably a bit late in the day for responding BUTÂÂÂÂÂ
There are lots of small evergreen tree available & when I say "tree" think bonsai!! IÂm going to try some heaths & heathers for the first time this winter IÂm not sure how happy they will be in window boxes but IÂm willing to try. I also had a hellebore in a container all winter last year. It was in an uninsulated sunroom easily visible from the armchair... beside the fire....Yea Hellebores.