I caution anyone with a debilitating disease to depend on a new crop of Nigella sativa also. As most know the ground is deprived of nutrients these days, some say up to 90% in some parts of the world. Trying to grow Nigella out of its natural surroundings has yet to be proven to be effective. These things are in trial.
According to the Plant Genetic Resource Program in Pakistan, they are now in the process of growing Nigella due to its high demand. You should begin planting your seeds in November, but you may grown them indoors in peat pots if you want. Keep in mind to start the planting prior to the first frost.
The rows should be 30 cm apart ( 10 to 12 inches) and the ground must be saturated deep with water.After about two weeks you should see the seeds germinate. If you want to grow them inside in peat pots do this prior to the autumn or spring and transplant them outside in your garden area 25 cm apart. Inside peat pots take around 7 weeks to germinate and grow big enough to transplant.
Once the flowers bloom, place the pods in a brown paper bag to dry out completely. Rub the pods in the bag with your hands to release the seeds. Cut a corner of the bag and let the seeds fall out into a sieve or filter of some kind. Sift them well and take the seeds and make sure the seeds are completely dry before storing them in an airtight container.
Ahmad, Z., A. Ghafoor, and M. Aslam. (2004). Nigella Sativa. A potential commodity in crop diversification traditionally used in healthcare. MINFAL. pp.34.