Hollies are familiar trees, easily recognized by their glossy, dark green foliage and beautiful bright red berries. But hollies are a diverse and varied group, and several species break from this mold. Although the vast majority of holly species are evergreen, a handful shed their leaves annually; some have spiny leaves, while others bear smooth, round foliage; and while bright red berries are iconic, some species bear yellow or black fruit.
Hundreds of species have been described worldwide, but a few – notably the American holly and European holly – are the most commonly used in ornamental plantings.
While holly fruits (technically, holly fruits are drupes, rather than berries) are toxic to humans and some domestic animals, a variety of wild creatures rely on them for a food source. Insects also feed on the nectar produced by holly flowers, and play an important role in fertilization.
Holly fruits develop from the late summer to the early winter, but most wild animals eschew the drupes until they’ve been through multiple freeze-and-thaw cycles. This appears to soften the previously hard fruits and make them more palatable.
In addition to providing value as a food source, hollies provide very dense cover to rodents and birds foraging amid their boughs. Nesting birds will also set up shop in these dense, often spiny, foliage.
Ornamental Use and Culture
Hollies are quite popular in the ornamental plant trade, and they are available as both wild-type plants and numerous human-created hybrids and cultivars.
Because most hollies are dioecious (plants occur as distinct male and female individuals), it is wise to plant representatives of both sexes to ensure the best possible fruit set. Additionally, while American hollies and a few other forms grow well in the shade, they will produce more fruit when grown in full sun.
Most hollies prefer well-drained, slightly acidic soils, but they are relatively flexible and will adapt to many different growing conditions. Different forms grow best in different places, and most locations have at least one species (typically many more) that will thrive in the area and climate. Taken collectively, hollies thrive in U.S.D.A. Hardiness Zones 3 through 11, which encompasses most of the country.
One down side to their ornamental use is the tendency of some to select non-native species. Most hollies, regardless of their point of origin, produce fruits that are attractive to local birds, who consume the drupes and deposit the seeds elsewhere. This often leads to the spread of invasive holly species, typically at the expense of native hollies and other understory species.
Selected Species Accounts
Species richness estimates for the genus Ilex vary widely. Some authorities recognize only 400 or 500 species, while others recognize nearly 800.
- American holly(Ilex opaca) – The American holly is an understory species of the southeastern United States, which occasionally grows to about 60 feet in height. When they are grown in open areas with full sun, American hollies often become impressive, pyramid-shaped trees. However, like many other hollies, American hollies are slow-growing trees that take a decade or more to reach maturity. A number of cultivars have been developed, including dwarf forms that make excellent hedges.
- European holly(Ilex aquifolium)– While European hollies are native to the warmer portions of Europe, their native range also extends into north Africa and southwest Asia.
- Winterberry (Ilex verticillata)–Winterberry is a large (occasionally reaching 15 feet in height or more), deciduous shrub, native to the Northeastern United States. Celebrated for its glorious red fruit, which are especially conspicuous given the lack of winter foliage, winterberries are a favorite of gardeners. A variety of cultivars are available, with varying tolerance for soil conditions.
- Mountain holly (Ilex mucronata) –The mountain holly was formerly called the false holly, and placed in the genus Nemopanthus, but recent molecular data has caused taxonomists to place it with the true hollies in the genus Ilex. A North American native, the mountain holly is a shrub that only rarely grows taller than 10 feet. It is sometimes grown as an ornamental shrub or in groups as a hedge.