Payments for Environmental Services (PESs) are increasingly used to foster farmers’ adoption of greener practices, but their effectiveness is often undermined by low enrollment. In a large randomized field experiment (N = 20,000), we test several non-monetary incentives to increase enrollment into the French implementation of the Agri-Environmental Schemes program of the European Union. We find that sending 10,000 information letters triggers the enrollment of 75 ± 52 farmers at a cost of 102 $\pm\ $71 Euros/new enrollee. Pre-stamped reply forms increase contacts with caseworkers but fail to raise enrollment. Testimonies by other farmers seem to decrease the effectiveness of the letters. Diffusion effects could increase the impact of our non-monetary incentives by 40% to 50% and decrease the cost of an additional enrollee by around 30%.