I have grown this in a container for the last 3 yrs. and recommend it highly. Mine faces south and is in full sun. I have to water daily in the summer, not at all in the winter. Every week or so I rotate the pot a quarter turn. I fertilize irregularly (as I do all over the garden). I don't trim it at all; its natural shape is quite lovely. It's now a little over 3' tall by 2' at its widest point. It has caused me no grief although I have found a few mealy bugs which were easy to smush. This is an excellent choice for a patio pot.
This boxwood is much hardier than merely zone 6. It is indeed one of the hardiest Buxus microphyllas, bred for cold tolerance. I have a three foot tall and two foot wide pyramidal specimen of this boxwood which survived -26 degrees last winter without protection other than snow which did not cover the top of the plant. Due to winter sunburn, part of the top was damaged, but new growth is now replacing the burned foliage. By next year it will have filled in. I will certainly use a burlap screen this coming winter. Three other Green Mountain cultivars, shaped into the typical round forms by pruning over the years, came through the same winter nearly unscathed and look as good as any grown in the South. Green Velvet is another hardy variety. Here in La Crosse, WI many people have started to plant several varieties of evergreen boxwood. Some have been growing here for 20 years. I suppose that if one winter we do drop below -35 degrees, which is a remote possibility here, many of these zone 5 and 6 plants, including the many Acer palmatum (Japanese maples) will perish or die back significantly. Because of these possibilities, zone hardiness ratings are on the conservative side, and perhaps should remain that way for those who wish to be certain a plant will survive the worst winter rigors their zone can muster. None of this will stop intrepid gardeners from experimenting with marginally hardy plants. To that end, I have just ordered a Stewartia koreana, a Magnolia grandiflora 'Edith Bogue' and a Sciadopitys. These plants will get plenty of tender loving care and will be planted in a well-mulched and protected site, but foraging deer and all-too-numerous rabbits may prove to be their worst winter enemies. My Japanese maples are tall enough now to evade deer, but the rabbits chew the bark off young trees in severe winters, just to survive, and survive off of our ornamental trees and plants they do. I will need to spend some time wrapping trees and ensuring they will be as rabbit-proof as possible. Wish me luck!
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