Why are there so few berries on my holly trees?
It’s true, some years there are more berries on our area holly bushes than others. There are several factors affecting this, beyond not having a suitable pollen source. These factors include a late spring frost, summer drought, late fertilization, biennial cycling, and unsynchronized bloom periods.
Late Spring Frost: As we know, this can and often happens in the Triangle area, and no one is every happy about it. When this occurs, many of the flowers drop, limiting the fruit set.
Late Fertilization: If we have a long winter and short spring, fertilization is often delayed. If this is the case, there is very little energy put into blooming, resulting in fewer flowers and thus, fewer berries.
Summer Drought: When water is in short supply, the berries are the first to suffer. During a drought, check to see if any developing fruit is wrinkled. If so, water deeply, or they will likely fall from the bush.
Biennial Cycling: The holly berries add important color to the winter landscape, but we want the birds to eat the fruit each year, and the cedar waxwings are notorious for this. If not eaten, the fruit remains, and little energy goes into blooming the following spring, plus there are less sites from which blooms can arise. The berries aren’t wasted, because the mocking birds will eat them in the summer, but then there is only get an every other year bumper crop.
Unsynchronized Bloom Periods: Various holly shrubs have bloom periods covering several months; some species have completed this process before other species begin. This is why it’s important to have a male of the same species for each of the female species grown.
How do I know if my holly shrub needs pollination?
Most hollies require a male holly to pollinate the female plant to insure fruit set. In other cases, the pollinator doesn’t need to be the same species, since flowering times overlap.
Here are some examples:
American holly, Ilex opaca, grows wild in open green spaces, so male pollen may be near by. To insure fruit set, add the male pollinator, Ilex opaca ‘Jersey Knight’, a male pollinator for American holly.
English holly, Ilex aquifolium, the male flowering time overlaps with the American holly, providing pollination. To fully insure berry production, plant the male English holly, Gold Coast, Ilex aquifolium ‘Monvila’.
Winterberry holly, Ilex verticillata, requires a male plant to bear noticeable numbers of fruit. ‘Apollo’, ‘Raritan Chief’, ‘Jim Dandy’, and ‘Southern Gentleman’ are companions to set fruit for the female Winterberry holly.
Foster holly, Ilex x attenuata ‘Fosteri’ and Savannah holly, Ilex x attenuata ‘Savannah’ typically get enough pollen from nearby American holly to set fruit; as does the Possumhaw holly, Ilex decidua.
In the case of the Chinese hollies, many don’t require a pollinator to set fruit, since some are parthenocarpic, setting berries without a pollinator. The resulting fruit is sterile, such as ’Burford’ holly, Ilex cornuta ‘Burfordii’ .
Nellie R. Stevens, Ilex x ‘Nellie R. Stevens’, is partially parthenocarpic. Better fruit set occurs when pollinated by a close-at-hand Ilex x ‘Edward J. Stevens’.
Yaupon holly, Ilex vomitoria seems to get enough pollen from unknown sources since they tend to berry and are not parthenocarpic. For more fruit production, ’Will Fleming’ is a male plant the help set more fruit.