Agriculture occupies more than a third of the world’s land with many, large-scale impacts on the environment and human health. This article investigates the failure of policy to manage these impacts, asks whether private law can fill the gap, and what this means for policymakers. The investigation takes the form of a case study of synthetic nitrogen fertilizer (SNF) in English policy and law. The SNF industry has been chosen because, by its own account, it underpins the modern food system, which is recognized as needing urgent transformation. The article first assesses the damage caused by SNF to health and the environment and the potential legal remedies. It then assesses industry claims that SNF (a) provides food security, (b) is beneficial to soil and water, and (c) reduces greenhouse gas emissions. If misleading, these representations could amount to unlawful ‘greenwashing’. While private law can never replace good policy and regulation, the article concludes that there is evidence to enable private law to supplement policy, and that this role is made possible as well as necessary by the absence of effective regulation and enforcement. Private litigation could catalyze policymakers to implement the robust regulatory regime that agriculture demands. As the law must focus on scientific evidence and causation, it can also help elucidate and publicize the science on which policy is based. Finally, because of the strict constraints within which private litigation must operate, it can direct policymakers towards strategic interventions (or tipping points) that could catalyze systemic change.