Four types of hemlock trees grow in North America, including the Eastern hemlock, the species with the largest distribution. Hemlocks are evergreen trees that have soft, flat needles and produce small woody cones that contain their seeds. Hemlock trees take as many as 200 to 300 years to mature and some specimens can live for as long as 1,000 years, states the Floridata website.
Eastern hemlock grows from southern Canada through New England and into the Appalachian Mountains. The tree grows as far west as the Great Lakes. Carolina hemlock has the smallest range of the North American hemlocks, growing in western parts of Virginia, the Carolinas and northeastern Georgia. Mountain hemlock and Western hemlock share a similar geographic range, growing along the Pacific Coast from California all the way north to southern Alaska.
The eastern hemlock and Carolina species grow between 40 and 70 feet high, with some individual trees getting much taller. Mountain hemlock can attain heights close to 100 feet where the tree has protection from the wind. Western hemlock is the tallest of the American hemlocks, averaging between 125 and 175 feet high, says the "Trees of North America" guide.
The needles of all American hemlock trees average under an inch in length but the size of the cones between species varies. Eastern hemlock has cones that are about 4/5 inch long, while Carolina hemlock cones are longer, at 1 1/2 inches. Western hemlock also has cones less than an inch in length, but mountain hemlock cones can be as long as 3 inches.
The shape of a hemlock tree is typically conical and the branches near the bottom can droop down and touch the ground. You may decide to trim the lower branches to give your hemlock a more open look. Hemlocks have scaly and furrowed bark that is purplish-brown or red-brown in color.
Hemlocks all grow in cool climates and the species does not do well in the heat. Plant a hemlock in partial shade for it to do well. The tree will not thrive in the full sun. Well-drained soils that are acidic, rocky and/or sandy will support hemlock trees.
Dry soils are not suitable for hemlocks; water the young seedlings often enough so that the ground they are in does not get a chance to dry out. It can take 20 years for a hemlock to reach a height of 40 feet.
Cultivars of the Eastern hemlock used for ornamental purposes include types like the Sargent's weeping hemlock, a shrub-like species that only grows 12 feet tall. This hybrid has long branches that bow towards the ground. The Aurea cultivar possesses yellowish needles. The Bennett variety is a dwarf hemlock that is just 5 feet tall and has the shape of a vase.