Holly, one of the traditional evergreens of the holidays, is a dioecious plant, which means holly plants are either male or female, and only the females have berries. In order to successfully produce seeds to propagate more plants, both sexes must grow in proximity to each other. Look for clues to the sex of the plant to guarantee berries on your holly bush.
Look at the leaves on the plant. Female holly tends to grow more leaves lower on the plant than male shrubs of the same variety and age. Leaves on male plants often exhibit fewer points.
Observe the trees when they bloom in the spring. Male blooms contain four insignificant petals with obvious extended pollen-laden anthers. Male holly flower centers are vacant.
Examine the fragrant white or pinkish flowers. Female plant flowers display four or five small petals. Insignificant sepals that hold no pollen stand around a distended four-chambered carpel that houses the plant's ovary.
Look for berries beginning in late summer on female plants. Most female plants produce red berries but some produce yellow or white berries; all are very hard and soften as the seeds ripen through the fall and into winter.
Ask the nursery operator when in doubt. There are dozens of varieties of holly; some respond to lack of presence of the opposite sex by developing complete flowers so they can self-pollinate and some have rounded, not the familiar spiny leaves.