- Wheat (Triticum aestivum L.) in Mediterranean regions is highly variable in end-use quality at the producer level. This study aimed to understand how sowing date affects wheat quality, especially gluten index (GI). Experiments were conducted in five fields over three consecutive seasons in 2009–2011. Twenty cultivars (four of which were common to all experiments) were sown from late October to mid-January on three dates (early, normal, and late) in each field. Grain yield, test weight, protein content,GI, sodium dodecyl sulfate (SDS) sedimentation, and alveograph parameters were analyzed. The GI of the four common cultivars showed a significant environment (experiment) × cultivar × sowing date interaction. In two experiments, GI increased with a delay in sowing; in two other experiments, a similar increase resulted from delaying sowing from the early to normal sowing dates but there was no further increase following late sowing or in one experiment where GI was unaffected by sowing date. Hence, delayed sowing mostly increased GI, except where weed or severe drought stress prevailed. Similarly, dough tenacity increased with delayed sowing. A high correlation was found among grain protein, wet gluten contents, SDS sedimentation, and alveograph index. Wheat GI was not a good predictor of quality and did not correlate with other parameters, whereas flour GI showed better correlations. Hence, we suggest delaying sowing (from late October to mid-January) to increase GI and that GI should be used with caution as a quality predictor. Instead of GI, using different methods may improve the determination of wheat quality.