Holly, a bush commonly planted as an ornamental, is dioecious, meaning that there are separate male and female plants. Many people pay no attention to whether they are planting a male or a female, but in order to produce the beautiful red berries for which holly is known, a female must first be pollinated with pollen from a male flower. In order to grow hollies that will form berries, it is important to know whether you have male or female holly trees in your yard or garden.
Look at the flowers of the plant when plant is in bloom. Blooms will appear in the spring, when holly plants produce flowers for the purposes of cross-pollination. Pollination of spring blooms makes possible the production of berries in the fall. Male flowers have distinct stamens, often in a cluster of four, arising from the centre of the bloom. Female flowers lack these stamens and instead have a green round bump in the middle of the flower.
Look for berries on the plant. In the absence of flowers, berries are another reliable identification method. If berries are present, you know you have a female. However, this rule does not work the other way. A plant without berries could be either a male or a female that is yet to be fertilised.
Look for any sort of tag, label, or name that identifies the individual tree as male or female when selecting from a nursery. In many cases, there will be no indication of which it is, and often names can be misleading. Generally, a name like Blue Prince indicates a male, while Blue Princess indicates a female, but other common names for holly varieties like Sky Pencil and Sparkleberry are less suggestive of the plant's sex. When in doubt, ask a nursery grower, who can clarify any confusion over holly varieties.