Ireland’s grass-based dairy system is relatively unique in industrialised countries in its focus on producing milk from grazed grass rather than increasing yields through non-forage feed. The environmental benefits of a grass-based dairy system have been promoted within Ireland and abroad. However, the means by which grass is produced is important. There have been environmental concerns about water pollution from nutrient leaching and increasing greenhouse gas emissions from the increased number of cows and higher fertiliser application in the Irish dairy sector. This paper uses qualitative interviews with Irish dairy farmers to assess: (1) how can we understand Irish farmer attitudes towards the grass-based system within a ‘good farmer’ theoretical framework? (2) How do concepts of extensive and intensive production fit with good farming norms within the grass-based system? (3) How could cultivation of multispecies swards, including legumes, fit with existing notions of good farming? The research finds that there had been a concerted efforts by researchers, advisory bodies and other actors to foster a definition of good farming to mean good grass management. This definition of good farming excluded the use of feed inputs over a certain level to increase yields but included the use of fertiliser to maximise grass production. There is scope to change the definition of good farming within the industry to include minimal use of fertiliser, for instance through the cultivation of multispecies swards including legumes and the skills and knowledge this involves. In terms of policy implications, the paper identified three strategies for government and industry to facilitate a definition of good farming which involves low fertiliser use: emphasising the cost-saving aspect of reducing fertiliser; identifying visible symbols of ‘good farming’ using multispecies swards; and co-producing the definition of good farming with a diverse range of stakeholders including farmers.