Winterberry holly Photo: Mike Masiuk, Penn State
Penn State Master Gardener Garden Hotlines receive the same questions each season. One of the most common questions in late fall concerns the lack of berries on holly.
Most hollies, Ilex spp., whether evergreen or deciduous, have male and female flowers on separate plants: hollies are dioecious. To obtain fruit set, the female requires a compatible male of the same or related species for proper pollination.
For the native evergreen American holly, Ilex opaca, one male can pollinate three female plants. Two reliable males are ‘Jersey Knight’ and ‘Big John’. ‘Jersey Princess’ and ‘Satyr Hill’ are popular female selections.
For the native deciduous winterberry, Ilex verticillata, one male can pollinate from five to ten female hollies. ‘Jim Dandy’ is an early male pollinator for northern types, and ‘Southern Gentleman’ is a pollinator for southern types. ‘Red Sprite’ and ‘Winter Red’ are good female selections.
For the hybrid, I. verticillata x serrata, the male ‘Apollo’ can pollinate ‘Sparkleberry’ and ‘Winter Red’. The male clone ‘Raritan Chief’ is used to pollinate many deciduous holly hybrids, as it flowers over a long period.
If a holly plant fails to produce berries, it is either a male (and will never produce berries) or it is an unfertilized female. There are several reasons why female hollies fail to produce berries, many of which are under the control of the gardener.
- Lack of a compatible male plant. A compatible male was not present within 100 yards (the range for bees to transfer pollen) while the female was in flower.
- Lack of pollinators. Insect pollinators (primarily honey bees) may have been too scarce due to loss of habitat or use of herbicides. There may have been reduced activity due to cold rainy weather during full bloom, thus reducing flowers and preventing fruit set.
- Immaturity. Hollies may take three to five years or more to bloom if grown from seed. Those grown from cuttings may take up to two years to bloom.
- Poor growing conditions. Hollies need moist, well-drained, acidic soil, in part shade to full sun. Lack of flower and berry production may be due to extremely dry sites, unprotected sites with exposure to desiccating winds and winter sun, heavy shade, and/or poor soil drainage.
- Improper fertilization. Excess nitrogen fertilizer, applied directly to the plant or even to adjacent turf, could have caused an overabundance of foliage at the expense of flowers and berries. Too little nitrogen could have also been a problem.
- Improper or heavy pruning. This may cause failure to flower and hence fruit set. Prune out dead, diseased or wayward branches at any time. Early summer is the best time to prune evergreen hollies, as they set buds the previous fall. A hard pruning after mid-July can force new growth, which may not harden off enough before the killing winter cold. Deciduous hollies bloom on new wood and may be pruned in late winter, but prune no more than 1/3 of the shrub at any one time.
- Uncooperative weather. Severe drought and/or high temperatures may have caused flowers or berries to drop. An early autumn frost or a particularly hard winter may have damaged tissue that was not fully hardened-off. A late frost in spring may have damaged flowers and prevented fruit set.
- Improper labeling. Your holly plant may not have been properly labeled at the nursery. Perhaps it is actually a male or is not compatible as a pollinator. To distinguish between male and female plants, examine the flowers. Male flowers have four stamens. They can be distinguished from female flowers which have a globose-rounded pistil.
Holly (Ilex aquifolium) flowers; male above, female below. Male flowers have four stamens and can be distinguished from female flowers, which have a globose-rounded pistil. Photo credit: Tigerente,CC BY-SA 3.0