Most of us have heard the story of Socrates and his untimely death at age 70. Standing before a jury and fellow Athenians, Socrates was sentenced to death in 339 BC. His anti-democratic views and impious acts lead to a guilty decision, a vote of 280 to 220, thus providing a suicide story for the ages. What most people don’t realize however, is that the poison hemlock consumed was not the evergreen type (Tsuga), but rather a deadly, poisonous herb of the Apiaceae family, (Conium maculatum). Mistaken for fennel, parsley or wild carrot, poison hemlock has tiny white flowers clustered in umbels. Native to Europe and the Mediterranean, poison hemlock, when crushed, emits a rank, unpleasant odor not the anise or liquorice smells associated with the likes of fennel. Suffice it to say, evergreen types of Hemlock look nothing like the herbaceous types.
These exact words were taken from an article I wrote for the Gardener News for my March 2007 column. At that time, Canadian (Eastern) Hemlock (Tsuga canadensis), had a “black eye” in the industry as its list of disease and insect problems was lengthy, most notably the infamous woolly adelgid. An insect native to Asia, the hemlock woolly adelgid is an invasive, aphid-like insect that has been attacking North American hemlocks for some time. Easily identifiable by the white woolly egg masses (ovisacs) they form on the underside of their branches and at the base of needles, this insect seemed to destroy retail sales for a much needed conifer. Resulting in severe needle loss, branch dieback and gray-tinted needles, this insect did enough damage, that even novice gardeners heard of its abuse. And while chemical insecticides prove useful for controlling woolly adelgid in a residential setting, they are not practical or economical in a forest setting. However, all this could change as there is a new hemlock hybrid on the horizon that withstands this killing insect.
Canadian (Eastern) Hemlock, (Tsuga canadensis), had long been a staple for our industry because of their tolerance to shady locations. A graceful evergreen that can offer significant value to most any situation. Useful as a single specimen or as a screen/hedge, there are many cultivars that lend themselves well to residential foundation plantings. Lustrous dark green needles with (2) whitish bands underneath are a great plant ID feature. Capable of growing 40-70 feet tall and 25-35 feet wide, hemlocks are “hardy” in zones 3-7(8). And while there are other conifer types that also tolerate some shade; Chamaecyparis, Cryptomeria, Microbiota, Sciadopitys, Taxus and Thujopsis, most of these simply don’t do it as well or may prove cost prohibitive?
Recently, Nursery Management magazine, one of many periodicals I subscribe to every month, let gardeners know that hope is on the horizon. ‘Traveler’, a hybrid hemlock, has been specifically bred for its resistance to hemlock woolly adelgid and has been selected for its notorious graceful, symmetrical appearance, complete with a slightly pendulous habit. The Agricultural Research Service’s (ARS) U.S National Arboretum developed this new variety, a cross between the Chinese hemlock (Tsuga chinensis) and the native Carolina hemlock (Tsuga caroliniana). The result has the native hemlock’s handsome, evergreen growth habit, complete with slightly weeping branches, a moderately slower growth rate and large cones. However, its greatest attribute purportedly, is its ability to “survive attack from the hemlock woolly adelgid”.
“Traveler” has been undergoing trials since 2000, and “we haven’t seen any damage from the insects despite the trees being planted out among susceptible Carolina and eastern hemlocks, said ARS horticulturist Susan Bentz.”
Woolly adelgid arrived in the United States in 1951 and has since made its way to many of our states. Important to note, while developing these hybrids, it is reported that the eastern hemlock would not cross with the Chinese hemlock, while the Carolina and Chinese types produced several offspring. “Hemlocks play important roles in forest ecosystems as well as in cultivated landscapes, serving as a foundation of species that impacts hydrologic cycles, wildlife, and biodiversity” (Nursery Management).
‘Traveler,” a slower grower, is both good and bad. Useful for residential landscapes, able to be clipped and hedged and survive shade and insects, it may not be economically feasible to use ‘Traveler’ routinely in forest renovations. A plant patent has been applied for and the ARS is steadfastly looking for commercial propagation partners to bring this exciting new plant to the nursery trade. I for one will be on the lookout for this plant in the coming years. Combing every plant catalogue, offering a graceful, shade tolerant conifer type, resistant to wooly adelgid, that will benefit our residential landscapes.