Introduction In the semi-arid regions of Southern Africa, livestock farming is a key source of livelihood, but its productivity is constrained by the availability of nutritionally adequate feed, a challenge exacerbated by climate change. The microalga Limnospira platensis (commonly known as Spirulina) presents a climate-smart alternative for producing good quality animal feed. However, its widespread use is limited by high production costs, particularly those associated with labour and cultivation media.Methods In this study, Spirulina CH22 was isolated from an alkaline soda lake in the African Rift Valley and cultivated using NPK fertilizer as a low-cost growth medium. Two formulations were evaluated: NPK alone (medium T1) and NPK supplemented with iron, magnesium, and calcium (medium T7). Zarrouk medium was used as the control. Biomass production, protein content, pigment concentration, growth rate, and cost efficiency were assessed.Results Cultivation in medium T1 resulted in lower biomass, protein, phycocyanin, and chlorophyll compared to the control. In contrast, supplementated media (medium T7) improved growth performance, yielding a 31% increase in biomass relative to Zarrouk medium, while maintaining comparable protein content (54% vs. 56%). Medium T7 also achieved a higher specific growth rate and shorter doubling time. However, chlorophyll and phycocyanin content were reduced by 25% and 27%, respectively, compared to the control. Cost analysis showed that medium T7 reduced growth medium costs by 63% based on local ingredient prices in Botswana.Discussion These findings demonstrate that NPK-based media supplemented with key micronutrients can significantly reduce production costs while maintaining high biomass productivity of Spirulina. Therefore, the use of medium T7 for the cultivation of Spirulina in Southern Africa could help to significantly lower production cost and encourage its wider use as food and animal feed source upon further nutritional and safety analysis.