Are they labled with a botanical name?? If we are talking about Viburnum
plicatum(japanese snowball Viburnum) the available cultivars do not produce
the snowball type flowers like the species does. The varieties that are
available in nurseries are actually Viburnum plicatum var. tomentosum, which is
suppsed to be a better choice than the species. Sounds like you purchased the
'summer snowflake' doublefile viburnum, especially since it is still
flowering in late september. If you dont have the desired flowers now, there
is nothing you can do.

Toad