Baptisia australis is a perennial wildflower that’s native to the eastern United States. A member of the Pea family, it has leaves and flowers that are are similar in appearance to those of garden peas and sweet peas. Although cultivars have been developed with blooms of various colours, Baptisia australis produces blue or purplish flowers. Colonial Americans used the flowers to produce a blue dye to use in place of true indigo (Indigofera tinctoria), which was expensive. For that reason, Baptisia australis is often called false indigo, blue wild indigo, or indigo weed.

Recognizing Baptisia australis

Native to the United States

According to the United States Department of Agriculture, false indigo is native to the eastern U. S. A. It grows naturally throughout the Central Great Plains and easterward, excluding Louisiana, Mississippi, and Florida. Although not native to Canada, it was introduced into Ontario. It now grows naturally throughout that province, even well into its northerly reaches. The University of Wisconsin-Madison Master Gardener Program explains that the plant typically grows wild in “prairies, meadows, open woods and along streams.”

Physical Characteristics

Baptisia australis grows slowly, in clumps. Over time, it takes on a shrub-like appearance. At maturity, it typically reaches a height and width both of about 1-1.2 m.

Each clump of false indigo has several slender stalks rising from the ground. The stalks have blue-green leaves that are about 5 cm in size. Each leaf is divided into three leaflets (trifoliate), like many other members of the Pea family.

False indigo’s flowers grow along racemes (spikes) that extend from 30 to 60 cm long. The flower spikes grow tall above the foliage and resemble lupine stalks. The blossoms, similar to those that grow on pea plants, range from pale blue to intense indigo and each is about 2.5 cm long. The plant usually blooms during spring or early summer. Bloom time is only about 2-3 weeks.

Spent blooms are replaced by seed pods that are very similar in appearance to pea pods. When mature, the pods turn black, which extends the plant’s ornamental value in home gardens. Loose seeds within the pods rattle around when moved by the wind. For this reason, the plant is sometimes called rattleweed or rattlebush.

Growing Baptisia australis

Starting from Seed

A piece by Mary Iannotti in The Spruce explains that false indigo can be difficult to start from seed. Replicating the way the plant self-seeds in nature, by scattering seeds in the fall, can work. Scarification or soaking the seeds in hot water may improve the germination rate. If started indoors, the seeds must be cold stratified. Once started, it will take 2-3 years for the plants to develop blooms.

Starting from Cuttings

The Home & Garden Information Center at Clemson University suggests starting plants from cuttings. Take cuttings in spring or early summer, while the growth is still somewhat soft. A section of cutting should be about 5-8 cm long and include at least one set of leaf buds. Dipping the cut end in a rooting hormone can help with the success rate.

Plant the cuttings in flats or pots. It’s important to keep the humidity high, so that the cuttings develop roots. Covering the plants with plastic tents or cloches and keeping them in a shaded area can help retain moisture. It will take about four weeks for roots to develop. Once rooted, the plants can be transplanted into the garden.

Preferred Growing Conditions

Although false indigo does best in full sun, it is not a picky plant. It tolerates drought and poor soil. Taller plants and those grown in shady areas tend to flop over and may need staking. The plant dies back in the winter and the foliage will droop. It’s recommended (but not required) that it be cut back in the fall. False indigo is cold hardy from Zones 3 to 10.

Possible Disease and Pest Issues

False indigo is susceptible to some fungal diseases. Powdery mildew, leaf spot, and rust can be issues if the plant is grown in damp or crowded conditions. As well, weevils may eat the seeds. This does not affect the plant’s health or appearance. But, if saving seeds, be sure to inspect them before storing.

Baptisia australis and Butterflies

The North American Butterfly Association reports that false indigo is a source of nectar for several different butterfly species. As well, the following butterfly species may choose false indigo as a food source for their larvae:

• Frosted Elfin (Callophrys irus)
  • According to the Government of Ontario website, frosted elfins are native to the eastern United States. They are found as far west as Minnesota and as far south as Alabama. The species had one known localized habitat in Canada, but hasn’t been seen there since 1988. It is not commonly found in gardens as its preferred habitat is oak savannas.
• Orange Sulfur (Colias eurytheme)
  • The Canadian Biodiversity Information Facility website reports that orange sulfurs are one of the most common butterflies in North America. They are particularly abundant in the southern U. S. A. They are also found in every province in Canada but not in the northern territories.
• Clouded Sulfur (Colias philodice)
  • Like orange sulfurs, clouded sulfur butterflies are very common in North America. They fly far north in Canada and are found in all provinces and territories.
• Hoary Edge Skipper (Achalarus lyciades)
  • According to the Canadian Biodiversity Information Facility website, hoary edge skippers primarily range from New York and Michigan in the United States down to northern Florida and east-central Texas. They are rarely found in Canada. Since the preferred habitat of this species is brushy or wooded areas, the butterflies are not commonly found in home gardens.
• Wild Indigo Duskywing (Erynnis baptisiae)
  • The Butterflies and Moths of North America website states that this species is found throughout the eastern United States, with a small number found in southern Ontario. They typically prefer open woods and meadows.
• Eastern Tailed-Blue (Everes comyntas)
  • The Canadian Biodiversity Information Facility website indicates that the eastern tailed-blue is common in southern Ontario, New Brunswick, and Quebec. In the U. S. A., this species is found throughout the eastern states.

While Baptisia australis can take some effort to establish and grows slowly, it is a striking plant. As an added incentive, it supports many different species of butterflies, both as a larval host plant and with its nectar for adult butterflies. Hardy from zones 3 to 10, it will grow almost anywhere in North America. If you’re creating a butterfly garden, why not include some false indigo?