Arboretum: Ilex opaca
American holly or Ilex opaca, one of the best known evergreens on the East Coast, is native from Massachusetts to Florida. It grows about 30 feet high into an erect and conical shape. The tree can be carefully pruned into a sharp outline or limbed up to allow for walking or planting underneath. But it will not grow back or “fill in” when branches are cut. A slow grower, holly prefers a sunny spot with well-drained, acidic soil. The plant can be used as a hedge, in a shrub border or as a specimen tree.
The species name opaca comes from the Latin opacus, meaning darkened or dull, referring to the plant’s dull green leaves. It’s natural for older leaves to turn yellow and drop in spring. Small, whitish-green and fragrant flowers appear in May and are easily overlooked. They lead, however, to the real reason people plant American holly, the showy red berries that appear in October and last through winter. Toxic to humans, the berries are a favorite for many songbirds, as well as squirrels and other small mammals.
Hollies are dioecious; a plant has either male or female flower parts. So for a good display of berries, a gardener needs to plant one male for every two to three female plants to ensure pollination.