Conventional polyethylene (PE) mulch has long been a staple in high value vegetable and berry production systems. It warms soil, conserves moisture, and suppresses weeds. However, its end-of-season removal and disposal can be labor-intensive and expensive. Soil contaminated PE mulch is rarely recyclable, and leftover fragments down into micro and nanoparticles, that persist in fields for years. Soil-biodegradable plastic mulch (BDM) films offer an alternative. These materials are designed to be tilled into the soil after harvest, where microbes convert them into carbon dioxide, water, and organic matter.

Commercially available BDMs are made from blend of biodegradable polymers - derived from plants such as corn starch (PLA, PHA), and from petro-based polymers (like PBAT or PBS). In addition, BDMs contain various additives, to improve their properties and performance, including plasticizers. The key distinction is that true BDMs are meant to biodegrade in soil, not just fragment like “oxo-degradable” plastics.

Research trials across crops such as tomatoes, peppers, broccoli, melons, strawberries, and pumpkins, have shown that BDMs can provide weed control and yields comparable to PE mulch. It is important to select a BDM film with the appropriate thickness for the crop’s growing season to ensure the film remains intact throughout the critical weed-free period. In heavy-fruit crops like pumpkin, mulch fragments can stick to fruit surfaces and affect market appearance. For fields with nutsedge pressure, note that both PE and plastic BDMs can be pierced; paper-based mulches often perform better for nutsedge suppression.

Degradation rates depend on temperature, soil moisture, and microbial activity. The warm conditions of the San Joaquin Valley favor faster breakdown once the film is tilled into the soil. However, real-world decomposition is slower than lab tests, so remnants may persist for more than two years before fully mineralizing. Short to medium term studies (up to four years) have found no significant effects of BDM use on soil health indicators such as pH, microbial activity, or organic matter. Unlike PE fragments, BDM residues continue to decompose over time and do not accumulate as microplastics.

Rolls of BDM typically cost 2-3 times more than PE but may offset by savings from skipping plastic removal and disposal at the end of growing season. Washington State University’s Mulch Calculator lets you plug in labor, disposal, and material costs to compare scenarios for your operation.

Organic Status: No commercially available plastic BDM is approved for certified organic production in the U.S. The National Organic Program requires BDM to be biobased determined using ASTM D6866 test; current products do not meet that requirement.

Trials are underway at the UC Kearney-REC in Parlier to evaluate BDM films under San Joaquin Valley conditions using strawberry as a model crop. If you’re seeking an alternative to plastic mulch, testing BDM on a few beds can be a practical next step. For on-farm trial support or specific questions about BDMs, contact Manpreet Singh at mansing@ucanr.edu or 559.646.6535.