Holly Berries and Pollination
The single most important thing to understand about holly is that it is dioecious — male and female flowers grow on separate plants, and only females bear berries, and only when a male grows nearby. This one fact explains most berry problems.
Why holly is different
Most flowering shrubs carry both male and female parts in every flower, so any single plant can fruit. Holly does not. It is dioecious (from the Greek for "two households"), meaning an individual holly is either male or female. Male hollies produce pollen but never berries; female hollies produce the berries, but only if their spring flowers are pollinated by a nearby male.
How to tell male from female holly
The difference shows in the flowers, which appear in spring. Both sexes have small white or greenish blooms, but a female flower has a plump central green ovary — the beginning of a future berry — while a male flower has several prominent pollen-bearing stamens and no central ovary. The simplest confirmation of all: a plant that has borne berries in the past is female.
How many males you need, and how close
One male holly can pollinate several females planted within roughly thirty to fifty feet, since bees carry the pollen. The male does not need to be the same cultivar, but it must be a compatible species and — importantly — it must bloom at the same time as the females. This is why winterberry is sold with matched pollinators: 'Jim Dandy' for early-blooming females, 'Southern Gentleman' for late ones.
Self-fertile hollies
A few hollies set fruit without a separate male. Chinese holly selections such as Burford and Dwarf Burford are famously self-fruitful, and Nellie R. Stevens fruits heavily even without a dedicated pollinator. Where space is tight and you want berries from a single plant, these are the reliable choices.
Other reasons a holly won't fruit
Beyond pollination, common causes of a berryless holly include a plant too young to flower (many take three to five years), heavy shade that suppresses bloom, a late-spring frost that kills the flowers, or over-pruning that removes the flowering wood. Correct the cause and, on a female with a male nearby, the berries return.