Western hemlock, native to the western parts of North America, is the largest of the hemlocks. Capable of standing deep shade, it grows in mixed forest on mountain slopes and forms dense stands. The crown is narrowly conical and the branches almost horizontal, though the leader and tips of the branches droop in typical hemlock fashion. The needles vary in length, growing outwards and upwards from the branches, covering them so that with age they appear from a distance to be covered in mossy layers.
In Europe, western hemlock is considered a tender maritime species, which is true if seed provenances from the Pacific coast are used. The first plantings of the species at Mustila were destroyed by the record frosts of the winter 1939-1940, when a young plantation of Alaskan provenance froze down to the snow level. However, a plantation of trees from seed of inland British Columbian provenance dating from the 1930s survived, and has now achieved logging dimensions – the tallest trees exceed 25 metres and they continue to grow robustly. Beneath and around the trees there are lots of naturally generated seedlings, which indicate that the provenance has adapted well to the site. There is a remarkable, impressive atmosphere in this wood, with faint light filtering through the thick layers of needles to the forest floor.
Based on experience at Mustila, western hemlock is the hardiest of the genus when seed of suitable provenance is used. The species is fairly undemanding regarding soil, but when young requires an upper canopy to protect it from the combined drying effects of spring sunshine and wind.