Many people seem to know that Socrates was sentenced to death by drinking poison hemlock. How this piece of trivia has remained resonant thousands of years later while so many important lessons are immediately forgotten is baffling, but every American should know that our trees of the genus Tsuga are not poisonous. They are wonderful members of our forests that are considered by many to be keystone species, and are not toxic at all (rather, the needles make a tasty tea). According to historical ecologist Dr. Chris Marshall, European settlers deduced that the tree was obviously evil because it was a denizen of land that was hard to farm and wasn’t as valuable for timber like many other conifer species they encountered. They named the tree “hemlock fir”, tying the hardy Tsuga to the poisonous herb, Conium maculatum, which the colonists knew and loathed from Europe. That being said, the following loving description is about the important trees, not the invasive herb.
Two species of hemlocks are found in the east: Carolina hemlock (Tsuga caroliniana), which is relegated to the high elevation forests of the southern Appalachians, and eastern hemlock (Tsuga canadensis), which is common across the northeast and in mountainous areas of the southeast. In silhouette, eastern hemlock is conical but the “terminal leader”, the stem at the very top of the tree, typically droops a bit rather than standing up straight. All branches are notably bendy and the entire tree can is often described as delicate, graceful, or feathery, setting the hemlock apart from spruces and firs, which are denser and stouter.
Up close, eastern hemlock needles are short and flat, with two parallel white lines on the underside of the leaf. Most needles are held to either side of the branch (as opposed to firs and spruces which typically have needles in all directions), but there are notably needles that sit on top of the branch, angling towards the branch tip. Each needle has a small stem that is attached to a woody peg that connects to the branch. Hemlock cones are small and delicate.
Eastern hemlock is a slow-growing tree that can tolerate shade and rocky, wet soil. It can grow to be 6 feet in diameter and 160 feet tall, and live for nearly 1000 years. Its slow, steady growth, even under a full canopy, results in its status as the “climax species” in much of New York, Pennsylvania, and West Virginia; in the absence of disturbance, a canopy of enormous, old hemlocks would dominate forest stands.
This mighty, beautiful tree is tough but has a notable weakness: the hemlock wooly adelgid. This invasive insect slowly weakens hemlocks by drinking their sap, usually resulting in the tree’s death within a decade. The beloved eastern hemlock (indeed, the state tree of Pennsylvania) is in big trouble due to this tiny insect. Cold winters set the adelgid back, and chemical treatments can help individual trees, but we are rapidly losing our hemlock forests, which have been keeping our mountain streams cold and clean for centuries. Genetic records show a severe bottleneck in hemlocks several thousand years ago, so perhaps there is a chance that this ancient genus will persist yet again.