Monrovia's Amethyst Falls American Wisteria details and information. Learn more about Monrovia plants and best practices for best possible plant performance. Wisteria Amethyst Falls has 12 inch elegant clusters of fragrant flowers. This is a noninvasive North America's Well-Behaved Wisteria. This wisteria variety is. Grow American Wisteria (Wisteria frutescens) to fill your garden with gorgeous Hardy to zone 5, ' Amethyst Falls ' blooms its first year—unlike its Asian cousins.