Baptisia 'Purple Smoke': Liners that Live and Flower.
Richard E. Bir
NC State University
Nature of work: Baptisia 'Purple Smoke' was discovered at the North Carolina Botanical Garden, Chapel Hill, NC by curator Rob Gardner. It is a putative hybrid of blue flowering Baptisia australis and white flowering Baptisia alba. 'Purple Smoke' flowers are smoky violet with the charcoal gray flower stems of Baptisia alba. It was introduced by Niche Gardens/North Carolina Botanical Garden in 1996. Propagation is accomplished via late softwood to semi-hardwood terminal stem cuttings. However, winter survival percentages were disappointing even when plants were placed in unheated white polyethylene-covered quonset structures for protection. Similar problems exist with other herbaceous perennials propagated by stem cuttings (1).
Cuttings from container grown stock plants were direct stuck and rooted under intermittent mist in Lerio 325 containers in a media comprised of 3:1 v/v pine bark:sphagnum peat with which 4.5 lbs dolomitic limestone and 2.5 lbs Esmigran had been thoroughly mixed per cu. yd. Fresh cut stem ends were dipped into a solution of C-Mone K at 1250 ppm IBA to a depth of 0.5 in. for a duration of 1 second prior to sticking. Half of the cuttings were stuck so that a bud was at least 0.25 in. beneath the propagating medium while half were stuck so that only internode, i.e., no bud, was beneath the propagating medium surface. Cuttings were stuck on May 8 and July 21, 2000. Cuttings rooted in an average of 4 weeks then were removed from mist, hardened off for a week, then fertilized with 0.25 tsp Sta Green 12-6-6 per pot.
Rooted cuttings were grown in the same containers in which they were rooted under overhead irrigation for the remainder of the 2000 growing season. They were allowed to go dormant naturally through exposure to ambient temperatures then moved to a white polyethylene covered winter protection structure until mid January when they were moved to a heated greenhouse, watered and encouraged to grow. One month after plants were moved into the greenhouse the percentage of plants showing new growth from each date and each treatment were recorded. 100% of all plants in this test started the winter alive.
Results and Discussion: Ninety percent or greater of plants survived winter from each sticking date if a vegetative bud existed beneath the propagating medium at the time cuttings were stuck (Table 1). Forty percent or less survived if no vegetative bud existed beneath the media surface.
By April, many of these plants were flowering in the greenhouse. Time of sticking cuttings was critical to flowering. No flowers existed on plants from the July sticking date. Plants from the May 8 sticking date had 50 percent flowering if a node was beneath the propagating medium while only 10 percent of those stuck on the same date with no node beneath the propagating medium flowered.
Significance to Industry: To successfully propagate and keep cuttings of Baptisia 'Purple Smoke' alive until the following spring, cuttings should be stuck so that a vegetative bud (node) is beneath the propagating medium surface. To have a significant number of liners flowering the spring following propagation, cuttings should be stuck in May rather than July.
Acknowledgement: Thanks to Niche Gardens, Chapel Hill, NC for providing stock plants for this test.
Literature Cited
1. Bir, R. E. and J. L. Conner. 1998. How and when herbaceous cuttings are stuck affects winter survival. Proc. SNA Res. Conf. 43:312-314.
Table 1. Percent survival of Baptisia 'Purple Smoke' following winter as influenced by location of vegetative buds and date of sticking.
| May 8 | July 21 | |
| Bud below media | 94 | 90 |
| No bud beneath media | 40 | 33 |
Return to Richard E. Bir homepage
North Carolina State University