It is an annual. Mine is blooming now. It is a late spring bloom. I do not water my garden and some years it does not come up, but this year I have three types of Nigella in bloom. It blooms at the same time as larkspur and can be planted at the same time as larkspur in late November and December. It wants some winter moisture to get it to Germinate. It got that this year here west of Austin. It grows in part sun/ part shade on a loose tree enriched soil over limestone . I think it would like a richer slightly more moist environment than what I give it. It is easy to grow and reseeds, or you can collect and replant.

Thank you so much for your information! I saw some blooming in a garden in Denton and I really liked them. This particular bed had chocolate daisy (berlandiera lyrata) blooming alongside the Nigella. The blue and yellow flowers looked really pretty together. I got seeds of the berlandiera, but will look for Nigella seeds later this summer for fall sowing.
Thanks again!
Molly

The bloom is not that long. Maybe if one pulls the pods off of them, one can prolong it.