Troubleshooting
Mountain Hemlock problems — and how to fix them
Mountain Hemlock (Tsuga mertensiana) is generally forgiving once you match its basics, but a few issues come up again and again. Here is what each one looks like, why it happens, and the fix.
Hemlock woolly adelgid
Though Mountain Hemlock has shown some resistance compared to Eastern Hemlock, woolly adelgid (Adelges tsugae) is an expanding threat as its range moves westward. Monitor branch bases for white woolly masses and treat with horticultural oil if detected.
Poor performance in lowland heat
Mountain Hemlock is adapted to cool, high-altitude climates. In warm, dry lowland gardens it suffers heat stress, needle browning, and decline. Situate in cool, north-facing or sheltered positions in warmer zones.
Windthrow on exposed sites
Although wind-hardy in its native habitat, in cultivation shallow root anchorage on thin soils can make large specimens vulnerable. Avoid exposure to strong prevailing winds and stake young trees during establishment.
Prevent mountain hemlock problems before they start
Most mountain hemlock issues are care-mismatch, not bad luck. Dial in the basics:
Looking for mountain hemlock in general rather than its problems? Read the full mountain hemlock care guide — light, water, soil and feeding.
Mountain Hemlock problems — FAQ
Why is my mountain hemlock hemlock woolly adelgid?
Though Mountain Hemlock has shown some resistance compared to Eastern Hemlock, woolly adelgid (Adelges tsugae) is an expanding threat as its range moves westward. Monitor branch bases for white woolly masses and treat with horticultural oil if detected.
Why is my mountain hemlock poor performance in lowland heat?
Mountain Hemlock is adapted to cool, high-altitude climates. In warm, dry lowland gardens it suffers heat stress, needle browning, and decline. Situate in cool, north-facing or sheltered positions in warmer zones.
Why is my mountain hemlock windthrow on exposed sites?
Although wind-hardy in its native habitat, in cultivation shallow root anchorage on thin soils can make large specimens vulnerable. Avoid exposure to strong prevailing winds and stake young trees during establishment.