Supplementary Material

Fig. S1. Comparison of temperature and relative humidity parameters across different planting months for two growing seasons (2020/2021 and 2021/2022) at Pretoria and Potchefstroom. (a) Mean maximum temperature (Tmax) and mean minimum temperature (Tmax) across all planting months from November to March (2020/2021). (b) Mean maximum temperature (Tmax) and mean minimum temperature (Tmax) across all planting months from November to March (2021/2022). (c) Mean relative humidity across all planting months from November to March. (d) Mean maximum temperature (Tmax) and mean minimum temperature (Tmax) across all planting months (November, January, and February; 2020/2021). (e) Mean maximum temperature (Tmax) and mean minimum temperature (Tmin) for selected planting months (November, January, and February; 2021/2022). (f) Mean relative humidity for selected planting months (November, January, and February). Temperature values are expressed in degrees Celsius (^∘C), and relative humidity is expressed as a percentage (%).

Fig. S2. Daily maximum and minimum temperatures recorded during the month of February 2021, Pretoria site. A heat wave occurred during this period on days highlighted by a light red box. These temperatures coincided with February and January planting dates at emergence and leaf development stages, respectively.

Fig. S3. Statistical analysis of plant height using ANOVA (P-value <0.05) and Tukey’s HSD test for multiple comparisons to test the effects of planting date and weather conditions weekly (from week four to week 11) across five planting dates (2020/2021) for season one at the Pretoria site. Significant differences between planting dates (row by column) with P-values <0.05 are highlighted in green filled blocks.

Fig. S4. Statistical analysis of plant height using ANOVA (P-value <0.05) and Tukey’s HSD test for multiple comparisons to test the effects of planting date and weather conditions weekly (from week four to eleven) across five planting dates for the second season (2021/2022) at the Pretoria site. Significant differences between planting dates (row by column) with P-values <0.05 are highlighted in green filled blocks.

Fig. S5. Statistical analysis of leaf number using ANOVA (P-value <0.05) and Tukey’s HSD test for multiple comparisons to test the effects of planting date and weather conditions weekly (from week four to eleven) across five planting dates for the second season (2020/2021) at Pretoria. Significant differences between planting dates (row by column) with P-values <0.05 are highlighted in green filled blocks.

Fig. S6. Statistical analysis of leaf number using ANOVA (P-value <0.05) and Tukey’s HSD test for multiple comparisons to test the effects of planting date and weather conditions weekly (from week four to eleven) across five planting dates for the second season (2021/2022) at the Pretoria site. Significant differences between planting dates (row by column) with P-values <0.05, are highlighted in green filled.

Fig. S7. The 100-seed weight (a), harvest index (b), and seed yield (c) for the 2020/2021 season; 100-seed weight (d), harvest index (e), and seed yield (f) for the 2021/2022 season at P = 0.05 of Potchefstroom site. The same letters on top of error bars indicate insignificant differences between planting dates using Tukey’s honestly significant difference; error bars represent standard errors and n = 3.

Table S1. Experimental design and trial plant for the 2020/2021 and 2021/2022 field seasons in Pretoria and Potchefstroom in South Africa.

Table S2. Levene’s test of equality of error variances a and b: (a) dependent variable—yield traits and seed yield and (b) design—intercept + planting date.

Table S3. Levene’s test of equality of error variances a and b: (a) dependent variable—yield traits and seed yield and (b) design—intercept + planting date.

Table S4. Levene’s test of equality of error variances a and b: (a) dependent variable—yield traits, seed yield, and seed quality and (b) design—intercept + planting date.

Table S5. Levene’s test of equality of error variances a and b: (a) dependent variable—yield traits and seed yield and (b) design—intercept + planting date.

Table S6. Levene’s test of equality of error variances a and b: (a) dependent variable—seed quality: oil%, protein%, linoleic%, and oleic% and (b) design—intercept + planting date.

Table S7. Levene’s test of equality of error variances a and b: (a) dependent variable—seed quality: oil%, protein%, linoleic%, and oleic% and (b) design—intercept + planting date.

Table S8. Levene’s test of equality of error variances a and b: (a) dependent variable—seed quality: oil%, protein%, linoleic%, and oleic% and (b) design—intercept + planting date.

Table S9. Levene’s test of equality of error variances a and b: (a) dependent variable—seed quality: oil%, protein%, linoleic%, and oleic% and (b) design—intercept + planting date.

Table S10. Total rainfall, mean maximum (Tx), and minimum temperature (Tn) during the grain filling (period from 50% flowering to harvest) stage across planting dates (PD) for two seasons and two locations.

Table S11. Effect of planting date (PD) and seasonal effects on sunflower yield, 100-seed weight, harvest index, and oil quantity and quality at the trial sites Pretoria and Potchefstroom (shaded grey) for the 2020/2021 and 2021/2022 growth seasons.

Table S12. Effects of planting date and weather conditions on total oil and linoleic acid content at trial sites Pretoria and Potchefstroom (shaded grey) for the 2020/2021 and 2021/2022 growth seasons.

© P. Mapfumo et al., Published by EDP Sciences, 2026