As with many out of zone plants, careful site selection is the key. I grew Green Mountain for a few years and it did well. The spot was on the north side of a low deck, in winter shade and loads of snowcover. Sometimes a few branch ends got burned after a winter but nothing major. Another interesting point was this spot was a low spot and fairly soggy during wet spells. Anyways, I only removed my boxwood because they are considered toxic and my puppy was going through an "chew everything" phase. Thankfully he's past that, but now I have ornamental grasses in that spot.

They are very attractive shrubs but I think in our zones they definitely need snowcover for the winter to protect the 'evergreen' leaves.

Glen

Glen, I have a protected north facing slope where I'll attempt a few varieties, they'll be shaded in the winter and hopefully shall receive the usual good bit of snow we get here. I might even try those styrofoam rose cones on them. Thanks for your comments Glen.

Terry

Green Mountain and Green Velvet are crosses of the Korean Littleleaf boxwood(Buxus microphylla var. koreana) and English boxwood(B. sempervirens), I believe. The former has the cold hardiness, the latter the better looking foliage. The results are excellent foliage with hardiness midway between.

So the Korean Littleleaf is the most cold hardy, but naturally turns a bit brownish in the winter before turning back to green in spring. The cultivar Wintergreen holds its green color through winter better.