'Clarendon Spreading' is a female cultivar of Ilex opaca selected for its dense, spreading habit, growing 3 to 4 feet tall and up to 8 feet wide. It is a broadleaf evergreen with the characteristic alternating spiny leaves of its species, gray-white bark that may be splotched or warty, and small dull green-white flowers in late spring. The bright red or orange fruits ripen in fall and persist well into winter, providing months of color interest at a scale that suits foundation plantings, slopes, and low hedges. Plants of this cultivar have been known to live to 80 years, giving a long return on the investment of patience.

As a female plant, it requires a male pollinizer, with one male typically sufficient for every six females. It shares the cultural requirements of the species: average, consistently moist, acidic, well-drained soil in full sun to part shade, with protection from cold winter winds and winter sun. Too much shade thins the foliage. Alkaline soils cause leaf drop, scorch, and chlorosis, and the usual holly pests, including leafminer, spider mites, scale, and whitefly, may occasionally appear. Its branches, laden with berries and spiny foliage, are a traditional choice for Christmas wreaths and it serves as a food source for the Henry's elfin butterfly caterpillar.