Abstract: For widespread adoption of biodegradable plastics as agricultural mulches, dependable biodegradation across contrasting conditions is necessary. The in situ degradation of four potentially biodegradable mulches (two commercially available starch-based films, one commercially available cellulose paper mulch, and one experimental spunbond polylactic acid mulch) were evaluated by measuring percent area remaining (PMAR) after burial for 6, 12, 18 and 24 months in high tunnel and open field tomato production systems at three geographically distinct U.