Answer: Keeping a Summer Snowflake pruned at only 4' will compromise its ability to set flowers and berries. Here's why - Summer Snowflake first blooms around the end of April or the first of May, about a week after dogwoods finish. The white flowers are individually about the size of a quarter, but borne in a flat head that is to four inches across. The blooms splayed on the horizontal branches give the plants a wedding-cake kind of look when they appear.
Other than the upright growth form (It can grow as tall as 15 feet but with a spread of only 6 feet), the other thing that sets Summer Snowflake apart from other viburnums is that it is a repeat bloomer. Admittedly, the first bloom of the season is much more showy than the ones to follow, but about once a month, additional blooms pop out here and there on the ends of new growth.
So, the problem with pruning it to keep it small is that no matter what time of year you prune, you'll be reducing or eliminating the flowering and berry set.
Wish I had better news for you!
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