With hollies, as with people, it takes two to tango. Almost all hollies (Ilex spp.) require both a male and female of the same species to set fruit. Some hollies, however, are parthenocarpic, or capable of self-pollination. Even self-fertile hollies will produce a heavier fruit set if a male holly that blooms at the same time is planted nearby.
The Burford cultivar of Chinese holly (I. cornuta "Burfordii") or the Burford holly, is a dense, rounded shrub or small tree that grows 15 to 25 feet high and wide if unpruned. Burford hollies have shiny, dark green leaves with a single spine at the end. The plants are covered in abundant, bright red fruit that attracts birds into the garden. There is a dwarf form, Burfordii Nana, that grows only 5 or 6 feet high and wide. The dwarf form doesn't fruit as heavily as regular Burford holly. Burford hollies are hardy in U.S. Department of Agriculture Zones 7 through 9.
Nellie R. Stevens Holly
Broadly pyramidal in form, Ilex x "Nellie R. Stevens" is a hybrid holly with the typical holly tree shape. The dark green, textured leaves have many spines, making this a good choice for a barrier plant. Nellie R. Stevens produces a heavy crop of bright red berries. The tree grows 30 to 40 feet tall and 10 to 15 feet wide, and stays densely branched to ground level. Nellie R. Stevens is hardy in zones 6 through 9.
Foster hollies (I. x attenuata "Fosteri") are crosses between two different holly species, I. cassine and I. opaca. The trees form 20-foot, conical specimens with narrow, shiny green leaves, and are useful for foundation plantings and in mixed borders. Some types of Foster hollies have been reported to be self-fertile, but since these types of hollies are quite variable, buy only from established garden centres that can advise you on which local cultivars are indeed parthenocarpic. Foster hollies are hardy in Zones 6 through 9, but that varies by cultivar.
Other Self-Fertile Hollies
The North Carolina Cooperative Extension service reports that the Bisexual culitvar of Nepal holly (I. integra) is self-pollinating, but little information is available on the cultivar. There is an older English holly cultivar, I. aquifolia "JC van Tol," that is self-pollinating, but difficult to find in the United States. Alaska is also reportedly self-pollinating but, again, is hard to find the United States.