Both. Kalonji nourishes the scalp with thymoquinone; Castor's ricinoleic acid strengthens follicles. Many users combine: kalonji 2x/week, castor 1x/week.
Kalonji is the scalp-health pick — its traditional strength is calming and purifying the environment hair grows from. Castor is the density pick for the hair itself. They blend beautifully: one part each in two parts almond oil makes a complete weekly treatment.