Some years the hollies will be loaded with berries while other years there are few holly berries to be seen.
1. Frozen blossoms or berries.
Late frosts can freeze holly blossoms or newly formed berries. Since Chinese hollies are so early to bloom, they are quite often damaged by late frosts, but some years even late-blooming Ilex opaca blossoms are frozen.
2. Summer drought.
When water is short the berries are first to suffer. They can be seen to develop wrinkles and if not watered immediately, begin to fall off the bush.
3. Late fertilization.
If the spring fertilization is delayed, there will be little energy to put into blooming – few blooms/few berries.
4. Biennial cycling.
If the cedar waxwings don’t get around to clearing your holly of old berries, there is little energy to go into blooming and few sites from which blooms can arise. Every other year, the berries on my Ilexx attenuata “Foster #2″ stay all summer due to the highly efficient protection provided by the resident pair of mockingbirds (1 mocker = 100 wax-wings!). The mockingbirds apparently like holly berries for dessert, about 5 per day, whereas waxwings can completely strip a holly in a matter of minutes.
5. Unsynchronized bloom periods.
Since the holly bloom period covers several months, some species have completed this process before other species begin. Also, although rare, there have been cases documented where the males and females of the same species are observed to bloom at different times.