Philip Crim
12-28-2022
Some plants are so ubiquitous and unassuming that we can see them almost every day without taking a moment to understand and appreciate them. Inkberry, Ilex glabra (L.) Gray, is one such species. A species of holly, it is valuable as a cold-hardy broadleaf evergreen, and the small stature and form of this species lends itself well to foundation plantings at residences, as well as more formal displays at businesses, the entrances to housing developments, and foundation plantings at home residences. Indeed, the ability of this species to retain its foliage and provide greenery deep into the winter season, even in northern areas, is an extremely valuable asset.
Although it may not look like a stereotypical holly to many observers, inkberry is exactly that. Hollies have gained wide familiarity due to the use of American (I. opaca Aiton) and English (I. aquifolium L.) hollies in holiday decorations. By contrast, inkberry has small, often obscurely-toothed oval leaves and purple to black fruits, for which it is named. Inkberry is not closely related to the group of hollies known for their spiny evergreen leaves and display of scarlet berries; instead, it belongs to a small clade of primarily central and South American species, with only two representatives stretching up to the Atlantic coast of the United States. A third representative of this group and close relative in the United States, the aptly named Ilex anomala, is native to Hawaii. These close tropical affinities make the cold-hardiness of inkberry both surprising and impressive, and the species occurs naturally along the eastern U.S. coast from gulf Texas all the way up to Nova Scotia.
In nature, inkberry is primarily a riparian species that is common in low wetlands, especially near the coast. While it is said to prefer acid soils and often grows upon/within them in native habitats, I have not observed any malnutrition effects such as chlorosis on cultivated plants where the soil is likely far more alkaline than those of its native haunts. Inkberry is a suckering shrub usually no taller than 10-feet in height; spreading by rhizomes, it can take advantage of disturbances such as fire by sprouting vigorously afterwards. The dense growth of inkberry colonies provides valuable habitat for many animals, and like other hollies the fruits are an important source of winter calories for many species. While the berries of holly species are inedible to humans, they are valuable as a late-season survival food near the end of winter.
In the landscape, inkberry is often touted as being resistant to deer browse, but in nature it is an adequate source of browse for white-tailed deer, especially in the winter (FS). In my experience, evergreen trees often become magnets for browse in northern areas, as they stand out like a sore (green) thumb late in the season. In areas with large deer populations, even species that are marginal sources of browse may be heavily damaged. While inkberry is not a deer “favorite” it is not viewed as marginal by the deer and I have seen it browsed heavily in New York, Pennsylvania, and West Virginia landscapes.
As an ornamental, inkberry has several valuable qualities. There are few cold-hardy broadleaf evergreen species capable of surviving in the American Midwest and Northeast, and many are so battered by winter conditions that they are hardly attractive. Inkberry is an exception and has been the subject of breeding and selection work since at least the 1930s. Depending on the seed source, some inkberries can tolerate temperatures lower than -20°F and -30°F. It is perhaps most similar in landscape attributes to the widely planted and non-native boxwoods (Buxus). Unlike many boxwoods, inkberry does not produce an unpleasant odor when sheared and is also less prune to ugly discoloration during the winter months. Most inkberry clones will discolor to some degree in winter, especially in more northern areas, but this often takes the form of an attractive bronze to purple shade that can actually be showy. Some plants tend to become “leggy,” and much breeding and selection work has focused on identifying clones that are more compact and less likely to exhibit this trait.
Like other hollies, inkberry is dioecious, meaning that male and female flowers occur on different plants and one plant of each gender must be present for fruit set. While this is a horticultural disadvantage for other hollies, inkberry is not generally planted for its fruit display; the generally purple or purple-black berries don’t pack the ornamental punch of other hollies, and the species is typically planted for its evergreen nature, dense habit, and pleasing form. There are a few exceptions, however; white-fruited clones have occasionally been found and some of these have been selected for ornamental use, although they probably fall more into the category of being curiosities. One drawback of the species is that it can be vulnerable to phytophthora.
While inkberry has many ornamental attributes, it is also an excellent plant for naturalization, restoration, and permaculture. Inkberry tolerates a wide range of soil pH and soil moisture levels, as long as conditions are not too extreme in one direction or another. The honey produced from inkberry is considered to be high-quality, and it fits well in mixed plantings designed to support pollinators. As noted above, the fruits can be an important late-season food source for many animals, especially birds. Although it is not a particularly close relative of another famous holly, yerba-maté (I. paraguariensis A.St.-Hil.), its leaves also contain caffeine and can be harvested for tea.
