I have a few native Viburnums but I never see any fruit. I planted them to feed birds. What is going on?
Ah yes, the complexities of native plants. Most nurseries and garden centers don’t tell you that almost all native viburnums need cross-pollination to set fruit (there are some exceptions). Retailers often suggest something like, “just buy several viburnums and you’ll be all set.” And so, off you go with your new plants, and later you wonder why your viburnums flower but never fruit.
Although viburnums are monoecious (plants have both male and female parts), they are pretty self-incompatible, requiring cross-pollination between at least two genetically different plants of the same species to set fruit in any quantity. Those genetically different plants must be in bloom at the same time so that visiting insect pollinators can do their job.
Don’t fall for the suggestion of simply buying a few of the same plants, like getting three Viburnum nudum, unless you know that they have all been grown from seed. If those plants have been grown from vegetative cuttings, they are clones and lack the genetic diversity needed for cross pollination and fruit set. In virtually all cases, viburnum cultivars are also clones.
What does this mean in practical terms? Look to purchase at least two genetically different viburnums of the same species. Straight species plants are best for biodiversity, but you may also consider cultivars. In most cases, simply planting two genetically diverse plants of the same species is enough to ensure fruit set. Viburnum dentatum is an exception – some cultivars bloom earlier than others. According to Gary Ladman, co-owner of Classic Viburnums, early blooming Viburnum dentatum cultivars include: Autumn Jazz, Blue Muffin, Cardinal and Little Joe. Later blooming cultivars include: Blue Blaze, Chicago Lustre, Northern Burgundy and Pathfinder. Make sure to buy different cultivars that bloom at the same time. Another approach would be to buy straight species Viburnum dentatum and a cultivar or two – again, making sure that they all bloom at the same time.
We should expect more from nurseries and garden centers selling native plants. Ask them the hard questions, and make sure that you are buying plants which will produce the ecological outcome you expect – in this case fruit for wildlife.
Hope that helps!
Kim Eierman at EcoBeneficial!