How to Tell Male from Female Holly
The surest sign is berries: only female holly bears fruit. To confirm before fruiting, look at the spring flowers — female flowers have a plump central green ovary, while male flowers have several pollen-bearing stamens and no central berry-to-be.
Because holly is dioecious, every plant is either male or female, and telling them apart is the key to getting berries. The easiest test is simply to watch through fall and winter: if a plant produces berries, it is female. A holly that never fruits, despite being healthy and mature, is either male or a female with no pollinator nearby.
To identify the sex earlier, examine the small flowers that open in spring. Both sexes bear clusters of little white or greenish blooms at the leaf joints, but the details differ. A female flower has a rounded green ovary at its center — the future berry — usually ringed by small non-functional stamens. A male flower has four or more prominent stamens tipped with pollen and no central ovary.
Plant tags and cultivar names also help: many holly cultivars are a known sex, and pollinator pairs make it explicit — 'Blue Prince' is male, 'Blue Princess' female; 'Jim Dandy' and 'Southern Gentleman' are male winterberry pollinators for female cultivars like 'Winter Red' and 'Berry Poppins.'