Summer Snowflake Viburnum. In April, this cultivar will be covered in white lacecap flower heads. But, its greatest attribute is that it continues to flower throughout the growing season. Even though this plant is not an extremely fast grower, it will nonetheless get quite large with age - in excess of 15'. But it can easily be kept at 6-8', and it is still a superb plant for long-season interest. Plant in full to filtered sun with good drainage and uniform moisture.