Wheat grain productivity is different from year to year because growing environments are highly seasonally variable as a result of climate change. This study analyzed the variation in the weather conditions in the 2010–2023 growing seasons and evaluated the crop developmental phase, yield-related components, and the correlations of the variables in the southern plain of South Korea, measuring agronomic traits, including the above-ground dry weight, young-panicle length, spike number per m2, number of grains per spike, thousand-grain weight, and grain yield. The number of days in the heading and ripening phase showed less differences than the other growth phases. The thousand-grain weight showed low variations over the fourteen years observed, unlike the number of grains per spike, the marketable grain yield, and the straw yield, with comparatively high variations. The grain yield was negatively correlated with the average air temperature during the winter dormancy phase (R = −0.687, p = 0.007) and precipitation (R = −0.726, p = 0.003), but showed positive associations with the number of days in the winter dormancy phase (R = 0.597, p = 0.024) and the number of grains per spike (R = 0.809, p = 0.000). In conclusion, longer winter dormancy and a longer tillering phase delay young-panicle development but increase the number of spikes and the number of grains per spike, resulting in a higher wheat grain yield in Southern Korean weather conditions.
