Gardening How-to Articles

False Indigo—A Spectacular Native Hybrid

Interest in native plants is soaring. All over the country, local native plant societies are educating people about the flora in their region. While I do not support the premise that native plants are the best or only plant solution and are "maintenance free," I am excited when gardeners see their local floras as viable choices for their gardens. Sadly, our wild plants are still more accepted if they go across the "big pond" and come back with a "proper" cultivar name to upgrade their status. By "native" plant, I mean plants that were in one of North America's ecological regions 150 to 200 years ago, before European settlers moved in and introduced new plants—many of which appear native today but, in fact, have only escaped cultivation and naturalized.

With the growing interest in and study of native plants, some forgotten ones are being reexamined for garden worthiness and occasionally a new selection of a native species is introduced. Such is the case with Baptisia 'Purple Smoke' or 'Purple Smoke' false indigo. Several years ago Rob Gardner, North Carolina Botanical Garden propagation curator, came across some unique seedlings—a natural hybrid of Baptisia australis with B. alba—in a row sown out in trial beds. Variations or hybrids occur naturally in the wild with this genus and apparently this happened in cultivation. Always looking for unique or deviant plants or ones that are different in some way, Rob was attracted by the unusual form and color of foliage and flowers. He grew it on, patiently observing it 3 to 4 years, before sharing his find.

Two in One

Imagine the rich blue pealike flowers of our blue false indigo (Baptisia australis) overlaid with the characteristic charcoal stems and gray-green foliage of white wild indigo (Baptisia alba), and you have 'Purple Smoke'. This unusual variation has the strengths of both native species. The flowers, an enchanting smoky violet with a purple eye, open first at the flower stalk base and ascend, topping out at four and one-half feet. Mature three- to four-year plants bear over 50 blooming stalks in spring gardens.

The genus Baptisia, which belongs in the Leguminosae or pea plant family, is made up of 30 to 35 species, all indigenous to the eastern and southern United States. Baptisia comes from the Greek word, bapto, meaning "to dye," which refers to one of the uses of the yellow-flowered species, B. tinctoria.

Baptisia australis, one of the parents of 'Purple Smoke', has thrice-divided, cloverlike leaves; the foliage forms a rounded mound out of which rise bright blue-flowering racemes. Native from Pennsylvania to Indiana and south to Georgia and Tennessee, B. australis occurs naturally in North Carolina on nutrient-poor soil with a high pH, generally 7 or above. When wet, this soil is sticky like molasses, but it dries out quickly in summer. The other parent of 'Purple Smoke', B. alba, is distinctive for its charcoal gray stems and contrasting milky white pealike flowers and grows naturally on a variety of soils from Virginia to Florida and west to Tennessee. In the wild, both species are often found dotting the landscape of open fields.

Native Americans made a tea from the roots of B. australis, used medicinally for emetic and purgative purposes. Today, scientists are investigating the plant as a potential immune system stimulant.

Patience Pays Off

'Purple Smoke' thrives in lean, well-drained soil in full sun and is hardy in USDA hardiness zones 4 to 9. It is truly a native plant selection worth its place in the garden for flower form, with spikes rising out of the foliage on one and one-half foot stalks; unique rich violet flower color; attractive small pealike bluish green leaves; and strong vertical upright form. In spring, sprouting stems resemble asparagus and quickly ascend three to three and one-half feet, out of which grow spires of flowers. Dark woody pods appear six to eight weeks after flowering. In Chapel Hill, NC (zone 7), 'Purple Smoke' along with B. australis and B. alba blooms for two to three weeks during April and May. In Brooklyn (zone 6) they bloom during May and June.

While most perennials mature and flower within one to two years after planting, Baptisia is a sleeper. During the first year, top growth is minimal, with energy spent developing an extensive tap root. In the second year, blooms shyly begin to appear with more flower stalks in the third year and by the fourth the plant becomes a show-stopping, shrublike perennial about four feet square with dramatic color. Cut plants back to the ground each fall after a hard frost blackens the stems. Once Baptisia is established, it will outlive you. The tap root digs in to make this plant a survivor in times of drought. The tap root also makes it chancy to divide or move. If changes need to be made, it is best to move other plants and leave the Baptisia where it is.

The round shape and vertical flower spikes of 'Purple Smoke' make a stunning accent in borders. It is an excellent companion planting for spring-blooming bulbs, Hubricht's blue star (Amsonia hubrichtii), Artemisia ludoviciana 'Valerie Finnis' and Nepeta mussinii 'Dropmore'. The spring chartreuse foliage of large Euphorbia species and golden feverfew (Chrysanthemum parthenium 'Aureum') acts as a foil for the bluish green of 'Purple Smoke'; and the bicolored orange-yellow flowers of our eastern native columbine (Aquilegia canadensis), or the yellow flowers of golden-spurred columbine (A. chrysantha) contrast strikingly with the darker flowers. Two honeysuckle vines, Lonicera x heckrottii and L. sempervirens 'Sulphurea', come to mind as colorful backdrops for the rich violet-purple flowers.

Propagation

Because it is a cultivar, B. 'Purple Smoke' will not reproduce true to form from seed. To propagate, take 1- to 2-inch tip cuttings from semi-soft or soft growth in late spring through early summer. Dip the cuttings in a powdered rooting hormone (or liquid rooting hormone at 1200ppm for five seconds); set them in flats or pots in a freely draining sterilized rooting medium in a shady area, protected from strong wind. To maintain high humidity, enclose flats in clear plastic and insert stakes to keep the plastic from touching cuttings. Mist the foliage once a day, if possible. Pot the cuttings after they have rooted—generally after about four weeks. Plant them directly into the garden in fall if they show tight dormant buds along the base of the stems. If not, overwinter in a protected area in the garden or in a cold frame. Mulch heavily.

At Niche Gardens in North Carolina, cuttings are kept in a greenhouse under 50 percent shade and misted every 10 minutes for 2 to 4 seconds. They are potted up by early July to give them sufficient time to grow on and establish a good root system and stem budding so that they can be planted outdoors in fall.

Propagation of Baptisia species is easy. In summer, pick the woody pods just as they begin to split open and remove the round brown seeds inside. Fill a cup with water heated almost to boiling, pour in the fresh seeds and soak overnight. To ensure full absorption, make sure the water covers the seeds. In the morning strain out and sow the seeds outdoors in a sterile commercial seed mix. Cold stratification is not necessary. To avoid crown rot or damping off, top off the seed mix with 1/2 inch of sharp sand or vermiculite; this keeps vulnerable young sprouting stems from rotting off due to excess moisture at the soil surface. Germination begins in two to three weeks with lingering sprouting thereafter.

Where to See It

At BBG, look for Baptisia australis in the Herb Garden and the Mixed Perennial Border, where you will also find a specimen of 'Purple Smoke'.

The North Carolina Botanical Garden displays 'Purple Smoke' in the mixed native Perennial Border.

Sources:

Rob Gardner
The North Carolina Botanical Garden
CB # 3375, Totten Center
Chapel Hill, NC, 27599-3375
919-962-0522

Niche Gardens
1111 Dawson Road
Chapel Hill, NC 27516
919-967-0078
www.nichegardens.com

Kim Hawkes is the owner of Niche Gardens, a nursery in Chapel Hill, North Carolina, specializing in nursery-propagated wildflowers, selected garden perennials, ornamental grasses, and underused trees and shrubs.

    Discussion

  • Laurel October 6, 2018

    In your discussion of Baptista propagation, you say to plant seeds outdoors in commercial seed mix. Is this a temporary step, or am I planting where the plants are to stay?

  • Joanne Griggs August 19, 2014

    From your article: “....sow the seeds outdoors in a sterile commercial seed mix…” Does this mean sow the seeds outdoors directly in the ground that has been amended with sterile seed mix, or does it mean sow the seeds in containers filled with sterile seed mix and place them outdoors? If planted in containers and placed outside, would you recommend that the containers be overwintered in a cold frame? Also, should the containers in a cold frame be further insulated by placing deeply into the ground? If pots are kept above ground, should they be surrounded by some other insulation? Thank you for a wonderful article and any info you can give me (I’m pretty much a beginner gardener).

  • Sally Boyce August 20, 2013

    Will false indigo survive in Florida?

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