Hemlock. I have been told that Hemlock attracts and harbours carpenter ants. Correct? Also how close to a home should you plant one? Is pruning to narrow the breadth of the tree advisable? Thank you.
Carpenter ants are normally associated with decaying wood, and will dig nests into dying Hemlock trees, hollowing large areas to house their larvae. A much more serious problem in the Eastern U. S. for the eastern Hemlock (Tsuga canadensis) is the woolly adelgid that kills the needles and prevents further growth. The Western Hemlock (Tsuga heterophylla) and the Mountain Hemlock (Tsuga mertensiana) are not affected by this pest. When planting a tree near the house it is necessary to consider the ultimate mature height of the tree and this will depend on which Hemlock you decide to acquire. The minimum space from the wall for small trees growing to 25 feet is 6 - 10 ft. or 5-8 ft. from the corner of a house. This would apply if you decided to acquire the weeping form of the Eastern Hemlock (Tsuga canadensis 'Sargentii' or 'Pendula') that grows 10 - 15 ft. and spreads 20-30 ft. It can be trimmed back to restrict its growth. Tsuga canadensis grows 40-80 ft. and would have to planted at least 15-20 ft. from the house. Similarly, T. heterophylla (Western Hemlock) grows 70 to 130 ft. and Mountain Hemlock to 50 ft. A dwarf cultivar of Western Hemlock called 'glauca' grows up to 10 ft. and spreads 6 ft. It has silvery green foliage. Hemlock cultivars can be pruned to control their growth as required. These trees are drought sensitive and require soil that is humous rich, moist, and well drained. I hope this helps.
I'll have to tell the western and mountain hemlocks here that the adelgids on them are not affecting them. The difference is that these two hemlock species are less readily killed by adelgids than eastern hemlocks--which are even being hammered in the remaining old growth stands--and not that they don't get them. There is a 'Glauca' cultivar of mountain hemlock, if western hemlock also has one it is so rare I have never heard of it--let alone is it likely to be found for purchase. Some wild-collected seedlings also become quite blue after spending a period of time in lowland cultivation--the opposite of what might be expected. Unselected individuals approaching/matching photos of 'Glauca' aren't rare.
Another suggestion for hemlocks close to a house- Tsuga heterophylla Iron Springs. This narrow cultivar usually reaches 8' as a 10 year old plant, which is about what a seedling mountain hemlock would grow. A good, slow growing cultivar of mountain hemlock that is very blue is Bump's Blue. We have both of these plants, in addition to numerous Tsuga canadensis cultivars in our garden (western Washington) and have had no problems with ants, and very little adelgid problems.
Sorry about the confusion with the cultivar 'glauca'. It is a cultivar of mountain hemlock, NOT Western Hemlock.
