If the Baptisia seed is sown fresh it can be sown directly into flats or an nursery bed. Plant seed ¼” deep. Fresh seed usually germinates within 2 weeks. That would be your basic 'winter sowing ' method.
For saved the seed needs to stratify/chill in the refrigerator for 6 to 12 weeks. After that scarify with sandpaper or a file, or nick seed coat with a sharp knife. Soak seeds in water for 24 hours before planting. Sow seeds in a well-drained seed mix. Provide bottom heat at 75 °F until plants emerge. In the Spring the small plants can be planted outside after last frost date, It may be least 2 to 3 years before seed-grown Baptisa make flowers, but your mileage may vary.