Answer: Male holly flowers are different from female holly flowers (of course, this limits identification to springtime, when both male holly and female holly come into bloom).
Both male hollies and female hollies bear flowers that have 4 petals -- so that's no help in identifying them. However, take a closer look at the flowers, specifically, at what protrudes from their centers. Male holly flowers have 4 yellow stamens; each female holly flower has a green ovary (that's the green "bump"). Once you determine whether your hollies are boys or girls, you can choose the right partner so you will get berries. Best wishes with your hollies!
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