Culture
Easily grown in acidic, medium moisture, well-drained soils in full sun to part shade. Best fruit production occurs in full sun, but plants generally appreciate some part afternoon shade in hot summer climates. Best sited in locations protected from cold winter winds. Avoid poorly drained soils. Mulch will help retain soil moisture and deter weed growth. Prune in winter if needed. Plants are dioecious (separate male and female plants). In order to set fruit, female plants will need a nearby male pollinator. Plants are not reliably winter hardy throughout USDA Zone 5.
Foster holly is one of the few hollies in which female plants will produce fruit without fertilization from a male pollinator. Botanically speaking, it is parthenocarpic (from Greek, parthenos meaning virgin and karpos meaning fruit). Therefore, it is unnecessary to purchase a male foster holly for a planting. Foster hollies are not reliably winter hardy throughout USDA Zone 5 and benefit from being sited in protected locations (particularly those sheltered from cold winter winds) in the St. Louis area (Zone 5b to 6a).
Noteworthy Characteristics
Ilex × attenuata is a naturally occuring hybrid originally found growing in the wild in Florida in 1924. It is a cross between I. cassine (dahoon) and I. opaca (American holly), both of which parents share native territory in the far southeastern U.S. (particularly from coastal North Carolina to Florida). This hybrid is a conical evergreen shrub or small tree that grows over time to 12-25’ tall or more, unless pruned shorter. It is commonly called topel holly, although some of the named cultivars thereunder have different common names (e.g. I. x attenuata 'Fosteri' plants are commonly called foster hollies). Hybrid cultivars grow in a variety of different forms and habits, but generally exhibit (a) spiny, elliptic to obovate-lanceolate evergreen leaves (to 3” long) with attenuated bases, (b) insignificant greenish-white spring flowers and (c) showy, pea-sized, red fruits that persists over winter. Fruits are ornamentally attractive. Birds are attracted to the fruit.
Genus name comes from the Latin name Quercus ilex for holm oak in reference to the foliage similarities (holm oak and many of the shrubs in the genus Ilex have evergreen leaves).
The hybrid name attenuata means narrowing to a point, possibly in reference to the growth habit of this hybrid.
Foster holly is the common name attached to five different interspecific hybrids (Ilex cassine x Ilex opaca) introduced into cultivation in the 1950s by E. E. Foster of Foster Nursery in Bessemer, Alabama. Of the five original clones, #1 and #5 are no longer available in commerce, #4 is a male which is uncommonly available (female Foster hollies do not require a male pollinator for fruit development) and #2 and #3 are female plants which are commonly available but are so similar in appearance as to be virtually indistinguishable. Although #2 is by far the most common female clone, nurseries sometimes sell the clones today as male or female Foster hollies without reference to clonal numbers. Foster #2 hollies are currently growing in the Hedge Display at the Kemper Center for Home Gardening. Foster #2 is a small to medium-sized, broadleaf evergreen tree with a dense, upright, pyramidal habit. It typically grows to a mature height of 20-30' tall with a spread of 10-15' unless pruned otherwise. Features glossy, dark olive green, elliptic to obovate, evergreen leaves (2-3" long). Each leaf has 1-5 well-spaced, tiny, spiny, marginal teeth per side. Small white flowers bloom in late spring. Flowers are followed in fall by an abundant and showy crop of bright red berry-like drupes which persist throughout the winter.
Problems
Potential insect problems include holly leaf miner, spittlebugs, spider mites, whitefly and scale. Potential disease problems include leaf spot, leaf rot, tar spot and powdery mildew. Plants are also susceptible to leaf drop, leaf scorch and chlorosis (yellowing of leaves in high pH soils).
