Seeds of Atropa belladonna were soaked for 12 h in a 1 ppm solution of gibberellic acid (GA3) in deionised water. They were subsequently surface sown directly onto coconut coir, watered from above with tap water and germinated in natural daylight at room temperature within a few weeks.
Soaking in a 500 ppm solution of GA3 for 24 h may leads to an even higher germination rate.
References
Asha Rani, N. S., and M. P. Prasad. “In-Vitro Studies on the Germination of Atropa Belladonna Seeds under Different Conditions.” International Journal of Science and Research (IJSR), vol. 3, no. 10, Oct. 2014, pp. 552–555., online.
Ruminska, A., et al. “Effect of Gibberellic Acid on Seeds Germination of some Vegetable and Medicinal Plants.” Acta Horticulturae, no. 73, 1978, pp. 131–136., doi:10.17660/actahortic.1978.73.18.