A common complaint about hollies is, “My hollies never produce berries; what I am doing wrong?” This can also a problem with some other garden shrubs.

Although most plants produce “perfect” flowers (i.e. having both male and female parts), a number of species are “dioecious”--male and female flowers grow on different plants.  So, in order to grow fruit on the female plants, one needs to plant males as well as females for pollination.  A ratio of one male for four or five female plants is usually sufficient.

It is often difficult to distinguish female flowers from male flowers without a hand lens. However, the sex of the plant should be indicated on the nursery label. Sometimes female and male plants will have different cultivar names, e.g. ‘China Boy’ and ‘China Girl’ hollies.

Here are some of the more common dioecious shrubs.

• Aucuba japonica (potted laurel) – not usually grown for fruit
• Ilex spp. (hollies) – Note that deciduous hollies, e. g. winterberry (I. verticillata), as well as the commonly planted English holly (I. aquifolium), are all dioecious.
• Juniperus  spp. (junipers) – not necessarily grown for their fruit, but the fruit adds winter interest.
• Lindera benzoin (spicebush)
• Myrica spp. (bayberry) - these plants are most often dioecious but some colonies are monoecious, with both male and female flowers on the same plant.
• Rhamnus cathartica (buckthorn) - highly invasive
• Ribes odoratum (clove currant)
• Taxus spp. (yews) – all parts of the plant are poisonous except the fleshy part of the fruit (arils).
• Viburnum spp. (viburnums) – Viburnums are monoecious, but you will get better fruits by planting plants from different sources. This is particularly true for V. davidii, which is often described as being dioecious.

Note: Many tree species are also dioecious.  A notable example is the ginkgo (Ginkgo bilboa)--only the male is planted in gardens, as the fruits have an unpleasant smell.

- Courtesy of NYBG Plant Information Service