Most hollies, whether deciduous or evergreen, require a male plant as a pollinator to insure fruit set. Though some hollies will set fruit in the absence of a male, the resulting berries will have sterile seeds.
English holly (Ilex aquifolium), American holly (I. opaca) and winterberry (I. verticillata) are holly species having male and female flowers borne on separate plants (dioecious). Female plants produce flowers without viable pollen, therefore, they are dependent upon male plants for pollination.
Pollen transfer from a male to a female plant is known as cross-pollination. If a holly plant fails to produce berries, it is either a male, or an unfertilized female plant. To insure good berry production, male and female plants generally should be of the same species.
Holly flowers have four, or rarely five, small white petals (Figure 1). The male flower has four prominent stamens, each composed of a filament (stalk) that supports an anther. The anthers release sticky yellow pollen. The ovary in male flowers is very small and not functional.
The female flower has a prominent pistil made up of a stigma, style, and a large green ovary. Female flowers may have underdeveloped stamens, but they will not produce viable pollen.
Holly flowers are cross-pollinated by insects such as bees and flies. Pollination takes place when pollen is transferred from the male anther to the female stigma.
When planting your holly orchard, locate your male plants equally among the female plants. Bees must be able to visit male and female flowers during the same excursion for cross pollination to occur. If bee activity is restricted by weather conditions during bloom, it may be necessary to double the number of pollinators (male plants).
The use of honey bees for pollination may be commercially feasible. Because holly is insect pollinated, hives of bees in or near the orchard will insure better fruit set (Figure 2).
Honey bees are unusually industrious insects. In a single day, one bee makes a dozen or more trips from the hive, visiting several thousand flowers. These numerous trips, coupled with the bee's hairy body, enables honey bees to accumulate and distribute an abundance of pollen. On each trip bees usually visit only one plant species, collecting one kind of nectar and distributing one kind of pollen.
Honey bees pollinate flowers more thoroughly within l00 yards of their colonies. Distribute honey bee colonies in groups throughout the orchard you want pollinated.
Beekeepers maintain honey bee colonies in most agricultural areas. They are usually equipped to move colonies easily and quickly to any location.
In orchards of less than 40 acres, place colonies along the borders of the orchard. In larger orchards, put colonies 528 feet apart in all directions. The exact number of colonies needed per acre may vary depending on the number of natural pollinators in the area, and on other crops competing for the attention of pollinating insects.
When bees are moved to new locations, they undergo a period of orientation as they get used to their new surroundings. Throughout this orientation time, bees are most effective pollinating flowers nearest the hive. Once fully oriented, their foraging extends further.
Before applying any pesticides to or near your hollies, read the labels to be sure that the pesticides won't be harmful to the bees. Whenever possible apply pesticides when bees are least active - from sunset until dawn.
Virginia Cooperative Extension materials are available for public use, re-print, or citation without further permission, provided the use includes credit to the author and to Virginia Cooperative Extension, Virginia Tech, and Virginia State University.
Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Alan L. Grant, Dean, College of Agriculture and Life Sciences; Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; Jewel E. Hairston, Administrator, 1890 Extension Program, Virginia State, Petersburg.
May 1, 2009