Gardeners have long appreciated false indigo, both the blue-flowered (Baptisia australis) and white-flowered (B. alba) kinds of these hardy perennials. Native to the eastern and southern United States, they produce pealike flowers on tall stalks in late spring. The white form is also notable for its charcoal gray stems and gray-green leaves.
Now a chance cross between the two species has been found at the University of North Carolina's Botanical Garden in Chapel Hill. This is a rare kind of horticultural good fortune in that the new plant combines its parents' traits beautifully.
'Purple Smoke' has the foliage of the white indigo and smoky blue flowers similar to its blue parent. It grows 4 feet tall and flowers for two to three weeks in early summer (in May in North Carolina). Even after flowering, the foliage and upright, rounded shape are attractive in a perennial border.
Like all false indigos, 'Purple Smoke' has a strong taproot, so it is long-lived and drought tolerant when established. It flowers best in fertile, well-drained soil in full sun. A 3- to 4-year-old plant can produce up to 50 flower stalks, which stand above the foliage for good viewing and make great cut flowers. 'Purple Smoke' is hardy in USDA Hardiness Zones 4 through 9 and is best planted in spring. It is widely available.