The aims of this paper are fourfold: (i) to review the scientific evidence of mixtures’ contributions to sustainable grassland systems, (ii) to derive guidelines on how to compose seed mixtures, (iii) to introduce a system of elite mixtures, the Swiss Standard Mixtures (SSM), as an exemplary case for the application of mixtures in farming practice, and (iv) to discuss the relevant factors for the success of the SSM system. For all these topics, there are fundamental differences between multi-species mixtures used for intensively managed, nutrient-rich grasslands and designed to efficiently produce high yields of high-quality forage on the one hand, and species-rich mixtures used for extensively managed, nutrient-poor grasslands that are designed to promote biodiversity at the levels of communities, species, and genotypes on the other hand. The advantages of mixtures are manifold, vast and robust, and thus they are an important pillar of sustainable grassland systems. The extent and the robustness of the advantages make mixtures a reliable tool for farming practice. The recipes of the SSM follow scientifically based guidelines, are developed in multi-site experiments and tested in on-farm trials. The system of SSM offers appropriate mixtures for a wide range of durations (one year to many years), production purposes (grazing and/or cutting; intensive or extensive; green forage, hay, silage) and growing conditions (wet to dry; favourable to harsh). The system has now been successfully applied for 70 years and has been continuously adapted and improved during these decades. The most important factor for this success is the tight collaboration among all stakeholders from research, extension, teaching, and seed industry under the umbrella of the Swiss Grassland Society (AGFF). This collaboration resulted in the AGFF quality label, which distinguishes high-quality seed mixtures.
