American Holly | Silvics of North America (2025)

Sexual Reproduction

Flowers, Pollination, and Fruit

Hollies are dioecious; male (staminate) and female (pistillate) flowers, similar in appearance, with four to six small white petals, are produced on separate plants on the current season's growth. The male-to-female ratio for 1,930 seedlings from 10 randomly chosen, open-pollinated pistillate trees was 1.03 to 1.00 after 9 years had elapsed and all seedlings had produced flowers. Flowering began as early as age 3 and the latest bloomed at age 9, staminate plants flowering somewhat earlier on the average than pistillate. For this reason, the male-to-female ratio at age 5 was about 5 to 1 (5).

Flowering begins in April in the southern part of the range of American holly, and in June at the northern limits. Pollination is accomplished by insects, including bees, wasps, ants, yellowjackets, and night-flying moths (3). Staminate trees should be planted close to fruit-producing trees (34). Although some female hollies are apparently isolated by distance from pollen-bearing trees, good fruit crops are produced regularly. The fruit, commonly called "berries," are technically four-seeded drupes or pyrenes. They ripen from September through December and remain on the tree through most of the winter unless consumed by birds or other wildlife. The fruit is round to ellipsoid, about 6 to 12 mm. (0.25 to 0.50 in) in diameter, and bright-but not shiny-red, orange, or occasionally yellow in color.

The four seeds in each fruit are bony with a coarsely reticulated, ridged surface (34). Seed germination is very slow, requiring from 16 months to 3 years in nature. Germination tests over a 2.5-year period indicated only 33 to 56 percent germination capacity. Overwinter storage or cold, moist stratification improves germination. Sowing immediately after collection has been recommended although complete germination does not occur until the second or third spring (4).

Seed Production and Dissemination

Seed production may be low in years of heavy spring rain, as rain can diminish the wide dissemination of pollen. A late frost can kill the spring flowers, eliminating a fruit crop. Frequent prescribed burning also drastically reduces fruit production. Such crop failures are rare and localized, however, and an abundance of seed can be found each year (19,24). Clean seeds average approximately 61,730/kg (28,000/lb) and about four units (by weight) of fruit yield one unit of clean seeds (4). Seeds are dispersed mainly by birds and small mammals.

Germination Requirements

Germination is epigeal. Following germination, holly seedlings rapidly develop a taproot and numerous lateral roots. American holly is very shade tolerant and may become established from bird droppings in the understory of upland pine plantations or bottom land hardwoods. It is very susceptible to fire and may be completely lacking in regularly or even occasionally burned forests (35). Initial growth is slow, averaging about 1.8 in (6 ft) in 16 years under medium shade (32). The bark is easily injured by fire and even large trees may be killed by light fires in the understory. Fastest growth of American holly was probably achieved in a North Carolina holly plantation; after 9 years of cultural practices such as mowing, mulching, and fertilizing, 10-year-old hollies averaged about 6.7 in (22 ft) in height and 3.7 in (12 ft) in crown spread and produced abundant fruit (24).

Asexual Reproduction

Vegetative Regeneration Requirements

Young holly trees usually sprout if the tops are removed by cutting or burning. Because of a taproot and a profilic lateral root system, young hollies can be transplanted without much difficulty (6). Transplanting should be done during the dormant season, usually November through March. Small plants may be dug bare-rooted if roots are kept moist, but larger plants should be balled and burlapped (34). When wild hollies are transplanted from the woods, tops should be severely pruned and most of the remaining leaves removed (16). Small trees should be allowed to flower before transplanting to ensure the selection of fruit-bearing individuals. Root pruning to a depth of 0.6 to 0.9 m (2 to 3 ft), a year before lifting, improves transplanting success (27). In Ohio, outside the natural range of American holly, better outplanting success has been obtained with plants 60 to 120 em (24 to 48 in) tall than those 30 cm (12 in) or less, because of winterkill of the younger plants (11). Holly can be produced from cuttings taken in August or September and December. Cuttings should be taken from the current season's ripened wood, with a small section of 2-year-old wood including several leaves. Cuttings should be set slanting in about 15 cm (6 in) of peatmoss and soil moisture, with the leaves lying flat on the surface. Treating with indolebutyric acid (IBA) and growing under high humidity with bottom heat is also recommended (6,24). "Quick dips" in IBA at high concentrations (up to 20,000 p/m) are recommended for cultivars that are normally hard to propagate (27). Root cuttings are unsatisfactory.

American Holly | Silvics of North America (2025)
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