Sunflower seed yield and quality stabilize across planting dates during hot, dry seasons under rainfed conditions in South Africa

South Africa is a water-scarce country predominantly practicing dryland agriculture, relying on rainfall onset to determine planting date. Sunflower is commonly considered a substitute crop, planted when primary crops face delayed plantings. The interaction between crop development and environmental variability is critical in Southern Africa because projections indicate warming of up to twice the rate of the global average. We investigated sunflower planting dates and production across two austral summer seasons (2020/2021 and 2021/2022) and two provinces of South Africa. A widely grown cultivar was sown monthly through the summer (from November to March) in a split-plot design. Plant height and leaf number were recorded weekly. Plants were harvested at physiological maturity for morphological and yield assessments. The hotter, drier first season (2020/2021 austral summer) led to the plantings reaching physiological maturity approximately 25 days earlier than in the wetter, cooler season (2021/2022 austral summer). In the hot/dry season, seed yield and quality were lower but more stable across planting dates. In the wetter/cooler second season, there were sharp declines in yield (78.8 g/plant, equivalent to 3.2 tons/ha ) and greater variation in oleic acid (up to 59.9%) across planting dates. These results highlight sunflowers’ stability under hot, dry conditions, supporting their use as a substitute crop.