I chose to write more about false indigo due to liking some photos of the post-flower seed pods. There is something about the beauty of those seed pods in the correct light (golden and late in the day) that works. Perennials that have little interest when out of bloom are of marginal value in most cases anyway (with apologies to the peony crowd).
About false indigo’s seed pods…they are not attractive to everybody. You can trim them back if you prefer. The seed pods do however give insight into the relation of false indigo to the pea family, as well as a path to new plants. False indigo does not divide nor transplant well, so if you want to make more false indigo without a visit to the nursery, you will need to learn how to harvest and grow new plants from seed.
Aside: In the past year, I’ve written about a number of different Baptisia species/cultivars: blue false indigo, Carolina Moonlight false indigo (my favorite), Twilite Prairieblues false indigo (not a favorite). More will be forthcoming to add to the list.
Growing false indigo from seed
Let the pods darken and begin to split open. Collect the seeds and broadcast them where you prefer new plants to grow. Baptisia needs winter’s chill (or a facsimile) to germinate. If you save the seeds to plant the following spring, you should chill for 6-12 weeks in your refrigerator. Scarify the seeds and soak in water 24 hours before planting (Clemson University Cooperative Extension bulletin 1184). Truthfully, rather than all the coddling and such I just broadcast the seeds when harvested and hope for the best.
It takes false indigo two to three years to flower.
Baptisia, Fabaceae: the pea family and nitrogen
Gardeners often comment about the similarities between the leaves of false indigo and peas, but photographs of Baptisia’s seed pods in the right light are truly reminiscent of peas. Like peas (and many other plant species) false indigo has the ability to turn nitrogen in the air (which is 78.1% nitrogen) into nitrogen available in the soil, a form of self-fertilization. People are most familiar with cover crops planted to create an influx of nitrogen into the garden and farm soil.
What I did not realize is that plants that fix nitrogen are classified by the USDA as low, medium, and high in the amount of nitrogen they actually contribute to the soil. An excellent overview of nitrogen fixation can be found at perennialsolutions.org.
False indigo is considered a medium nitrogen fixer (85-160 pounds/acre)…native plants that actually improve the soil in which they are grown.