In our cold and crispy climate it is little wonder there is going to be a certain amount of winterkill. Boxwood is a plant that most people don't think grows here (in zone 3 Calgary) but - in fact - it can be quite good in a sheltered east or semi-shade location. The tiny bit of winterkill showing here is easily removed at this time of year. Check out my Calgary Herald article on May 15 for a full article on spring pruning to remove winterkill and other such things.... Yes it is gardening season again at the Herald so don't miss out.
