Wild Blue Indigo

Baptisia australis is a native North American prairie and woodland-edge perennial in the legume family — a deep-rooted, warm-season plant that spreads by seed or by short rhizomes. It grows erect and bushy, with stout, smooth stems and alternate, three-part blue-gray-green leaves, reaching up to five feet tall and three feet wide but more often around three feet by two. From April through June it carries erect terminal racemes of inch-long pea flowers that range from light blue to deep violet-purple. Once established, plants are extremely long-lived and need virtually no maintenance; herbicides aimed at broadleaf weeds will kill them, so keep spray well away.

The blue flowers give way to inflated, hardened pods, one to three inches long, that dry to charcoal black with the small seeds loose inside — shake a dry stem and it rattles, which is why the plant has long been called rattlepod or rattlebush; Native children used the dried pods as toy rattles. The pods are prized in dried arrangements, but the plant makes a poor fresh-cut flower: the blooms and stems blacken almost as soon as they begin to dry. Snap a leaf or stem in the growing season and the sap turns slate blue in the air. In autumn the whole plant fades to silvery-gray and breaks off at ground level, then tumbles in the wind like a tumbleweed, scattering seed as it goes.

The common name 'false indigo' marks it apart from true indigo (Indigofera tinctoria), the Asian dye plant grown by early American planters. The Cherokee used Baptisia as a source of blue dye for clothing and pioneer settlers copied the practice. Several tribes also used it medicinally: the Osage made an eyewash from it, the Cherokee brewed a tea — taken hot as a purgative, cold to settle the stomach — and a pulverized root or hot tea was held against a sore tooth for the pain. The plant contains bitter quinolizidine alkaloids (anagyrine, cytisine, sparteine and others) that make it unpalatable to grazing animals and can cause diarrhea and loss of appetite in livestock; no poisonings of people or pets are on record, but it is not for internal self-treatment. Modern German research suggests some Baptisia species may stimulate the human immune system.

The plant sends down a deep, woody taproot and is slow to establish — expect three to five years before a newly set plant blooms reliably, and never try to divide or transplant an established one. Root tubercles fix atmospheric nitrogen, gradually enriching the surrounding soil. It wants full sun and gravelly, sandy or well-drained loam, withstands prolonged drought, and is cold-hardy to about -30°F (USDA zones 3 to 10); it does not grow in shade. The hard seed coat must be broken before it will sprout in cultivation: scarify the seed, then cold-moist stratify and soak it a full day before sowing, and expect germination once the soil nears 50°F. Seed gathered from the wild germinates poorly because weevils routinely bore into the pods, so treat or sort collected seed before storing it. Native from Nebraska and Texas east to the seaboard and north into Canada — New Hampshire is its far northeastern limit — it is rarely found near the coasts and is listed as threatened in several states. It serves as the sole larval host for the wild indigo duskywing butterfly (Erynnis baptisiae) and supports multiple specialist native bee species.