Is Snowball Viburnum tolerant of Black Walnut?
There are several viburnums that are referred to as "snowball" but this name is most commonly associated with Viburnum opulus. While some viburnums are sensitive to juglone in the soil, many are not and it would be good to confirm that we are talking about the right type of shrub.
If you have a Viburnum opulus, it will be sensitive to juglone and should not be planted under a black walnut tree. Here is a link to a good list of juglone sensitive plants from Michigan State University Cooperative Extension.
Courtesy of NYBG Plant Information