Ask Mr. Smarty Plants

This question came up fairly recently, with the same cultivar, 'Blue Muffin', of Viburnum dentatum (southern arrowwood) as the ones you have just obtained. Here is a quotation from a previous answer. 

"Many plants exhibit self-incompatibility—a genetic trait produced by a gene that creates a chemical barrier when the pollen of a genetically identical plant falls on the carpel (female part). This chemical barrier prohibits the pollen from fertilizing the ovules and there will be no fruit.  V. dentatum plants are commonly propagated vegetatively from cuttings.  If they are propagated from the same stock, such as your cultivar "Blue Muffin" must have been, they are going to be genetically identical—in other words, clones.  So, you do need at least one plant that isn't a clone of your "Blue Muffin" plants to produce pollen that won't be chemically barred from fertilizing your flowers. The University of Connecticut site lists 8 cultivars of V. dentatum, including your "Blue Muffin", so there are other possibilities.  I recommend that you visit our National Suppliers Directory and enter your city to find nurseries in your area that specialize in native plants.  You can visit their websites (if they list one) and/or telephone them to find out what cultivars they carry of V. dentatum.  Just to be on the safe side you might buy two completely different cultivars to plant."

The tricky thing is that Viburnum are monoecious, meaning that there are both male and female flowers on each bush. But, because when you buy two bushes of a single cultivar, they are both clones, you need at least one Viburnum of a different cultivar (although it will still be a clone, just not of the same cultivar) in order to get berries.

Since the 'Blue Muffin" cultivar is apparently a smaller version of Viburnum dentatum, it sounds as though it is already big enough to begin flowering in the spring, followed by berries IF you have obtained another sub-species or cultivar and it is pollinating at the same time.The Viburnum is hardy from USDA Hardiness Zones 3 to 8, and Kansas City, in Northeastern Kansas, appears to be Zone 5b, you shouldn't worry too much about pruning in the winter, but mulch is always a good idea, protecting the roots from both heat and cold, and helping to keep moisture in the soil. 

Pictures of Viburnum dentatum, including 'Blue Muffin' with berries

Viburnum dentatum

Viburnum dentatum

Viburnum dentatum