Getting Viburnums to bear Fruit

Last year I posted a blog on how using cloned plants may reduce the viability of seed produced in the garden. In some cases this is not a bad thing from a design point of view, if it is desirable to limit the number of ‘spontaneous’ seedlings and maintain a 'clean' ground plane. If your goal is to produce seeds and berries for wildlife, then the use of sterile, or self-sterile plants is of no advantage. The situation that brought this up was that the Viburnum nudum ‘Winterthur’ that I have has never produced more than a couple of small berries each year. After 5 years of this I investigated the situation and leaned that in order for Viburnums to produce seed it must be pollinated by a genetically distinct individual. (You see most cultivars are clones of the same individual.)  So last summer I picked up a straight species form of Viburnum nudum and planted it nearby.

These pale green berries will turn pink, then dark blue as they ripen.

This year I’ve got many, many more berries forming on the ‘Winterthur’, as well as the species plant. The species and ‘Winterthur’ bloomed at the same time; this is very important for cross-pollination. There is a difference in form and fall color between the two plants. ‘Winterthur’ is more upright and the fall colors on a single plant vary from light orange to red. The species plant is more lax and turn a rich burgundy color in the fall. Now I’m looking forward to seeing some of those brightly colored berries later in the fall.

Fall color for 'Winterthur' cultivar

Viburnum nudum species in early November.



Only a few of the signature blue berries
matured on this lone Arrowwood Viburnum.



Earlier this year I also added an Arrowwood Viburnum, Viburnum dentatum ‘Christom’= Blue Muffin®, to fill a gap in a shrub border. To my knowledge there are no other Arrowwoods in the neighborhood. This species of viburnum blooms 3-4 weeks earlier than the ‘Winterthur’ and only two clusters of late blooms overlapped with the opening of the flowers on the ‘Winterthur’. On inspection today, the Arrowwood has just a few mature berries on the plant, all of the other flowers just fell off shortly after blooming. So it may be that the pollen from these two species is compatible, but their blooming times are so different that they are not practical mates.

In any case, now when I recommend Viburnums in a wildlife-friendly garden, I try to include two different cultivars of the same species, or look to see if there are some other plants of the same species growing nearby. I will need to look for a chart with bloom times for all of the Viburnums to see if there any other possibilities for interspecies compatibility, as is done with Holly.