The holly (ilex) family has 400 members. While there are similarities among all of them, there are also differences. Not all of the varieties are readily available to the home gardener. The ones that are available have been specifically cultivated for the garden and have been bred to grow in a garden environment.
Holly trees and bushes are either male or female. Both are needed to produce the berries. The ratio of male to female plants varies by the variety. Hollies are broadleaf evergreens or deciduous plants with spiny, pointed leaves in a wide variety of sizes and shapes. The berries are toxic to humans and the plants should not be placed where children can get to them.
Japanese holly (Ilex crenata 'Sky Pencil') is a female cultivar and needs a male of another variety to produce fruit. Possumhaw (Ilex decidua) is a deciduous shrub native to the southeastern and central United States. Blue holly (Ilex x meserveae) is also known as meserve holly. The plant is an evergreen shrub.
Japanese holly grows from 4 to 10 feet tall and 1 to 3 feet wide. The tree features elliptic or egg-shaped, small dark-green leaves measuring from ½ to 1-1/4 inches long. Tiny, green-white flowers bloom in May and June and produce purple berries 1/4 inch wide in the fall.
Possumhaw reaches a height of 7 to 15 feet with a spread of 5 to 12 feet. White flowers bloom in May. The flowers on the female plant produce orange-red berries in September. The fruit stays on the tree until the following March. Narrow, egg-shaped, glossy dark-green leaves measure 2 to 3 inches long and turn a purple green to yellow in the fall.
Blue holly measures 8 feet tall by 8 feet wide with blue-green, evergreen, elliptical-shaped leaves up to 3 inches long. Cream-colored flowers grow in clusters from May through the fall. Female flowers produce green berries that mature to red or yellow and stay on the shrub through the winter.
Japanese holly is hardy in USDA zones 4 to 6. The plant likes full sun or partial shade and a soil that is average and well drained. The tree is tolerant of urban pollution. Possumhaw likes full sun or partial shade and a soil that is moist and organic. The plant is hardy in zones 5 to 9. Blue holly prefers partial shade but can go in full sun or full shade if necessary. Plant in a rich, moist, well-drained soil. The shrub is hardy in zones 5 through 8.
The leaves of the Japanese holly turn yellow if the soil is too alkaline. The tree should get a winter mulch in the northern end of its zones. Spider mites and nematodes cause problems. Possumhaw is occasionally bothered by leaf spots and powdery mildew. Blue holly suffers from foliage and stem burn in winter and heat stress in hot, dry summers.
Use Japanese holly in small narrow spaces, as a specimen plant or as a tall, thin hedge or privacy screen. Birds, deer, opossums and other small mammals make a meal out of the berries of the possumhaw. Plant possumhaw as a specimen plant, in groups, as a hedge and along the banks of ponds or streams. Blue holly is used as a foundation plant, in groups, as a specimen plant or as a formal or informal hedge.