In the face of climate change, improving yield stability is critical for food production systems. Increasing diversity in agricultural systems can be a way to stabilize yield across time and/or space. This can be done with mixtures of varieties, which represent a practical way to introduce diversity at the genotype level in agricultural fields. However, in Switzerland, wheat variety mixtures are still rarely used, due to a lack of understanding of the processes driving yield benefits and, consequently, no clear rules as to which varieties to combine. In this study, we used results from a Swiss wheat variety mixture trial to investigate the drivers of mixture productivity and stability. We hypothesized that mixtures composed of more different varieties – in terms of genetic distance but also of morphological, agronomic or synchronicity aspects – would be more productive and/or stable. We did not find any effects of genetic distance on mixture productivity or stability, but we did observe an increase in mixture stability with reduced synchrony of the components, i.e. when the components reacted differently to environmental conditions. This result was only significant in the first year of the trial, which was less productive due to more stressful conditions. This study shows that when combining asynchronous varieties, wheat variety mixtures have the potential to buffer possible yield losses due to external stressors during suboptimal years. While more research is needed to confirm this result, variety mixtures nonetheless represent a promising solution to sustainably increase the stability of wheat production in Switzerland.