Viper performs. Independent trials have proven that F1 Viper will give you the hybrid advantage. F1 Viper is the king of vinca - vigorous, robust plants give the ultimate 4-6" (10-12cm) pots and garden performance. In the landscape Viper grows into a large mounded plant covered in massive flowers with overlapping petals. No other vinca can match F1 Viper in the landscape. The vigorous well-branched plants continue to perform through extreme hot and humid conditions.