Asked January 08, 2015, 10:45 AM EST
Washington County Pennsylvania
Thank you for your patience.
Canadian Hemlock (Tsuga canadensis) will continue to be stressed by Hemlock Woolly adelgid, which may have already arrived in your area.
I would consider alternative species suitable for your site and purposes. If you want a year-around visual screen, perhaps White Pine (Pinus strobus) is still a native tree which would serve you well. Another from ranges south of you is Atlantic White Cedar, (Chamaecyparis thyoides).
If you really want to continue with hemlock, you may consider the Carolina Hemlock (Tsuga caroliniana), native to further south. It may be more heat tolerant, and perhaps will withstand stresses inclining the Canadian Hemlock to Woolly adelgid attack.