Update on Soil Biodegradable Mulches

Biodegradable mulches are a promising alternative to traditional polyethene plastic mulches that reduce plastic waste generation and provide opportunities to reduce the costs of mulch removal and disposal. They are currently being investigated in strawberry systems in collaboration with the University of California Extension, Monterey Bay National Marine Sanctuary, Cal Poly, and Washington State University.

Since we are investigating this technology here in California, look to this blog for occasional developments in research and regulation in soil biodegradable mulches.

The State of California recently set standards for soil biodegradable mulches:

“Biodegradable” is a term that is often associated with environmental stewardship and sustainability. Unfortunately, it is also a descriptor that has been abused and manipulated by plastic manufacturing companies that used it for marketing purposes. This was done by selling materials labeled as “biodegradable”, even though they were not biodegradable and did not meet scientific standards for degradability.  An example strawberry growers may be familiar from years past would be oxo-degradable and photo-degradable mulches, which were falsely sold as biodegradable mulches. These mulches are not truly biodegradable, simply fragmented into smaller plastic pieces and that contributed to soil pollution. 

Truly sustainable mulch alternatives DO exist and their credibility just got a boost in September 2020 when the California legislature and Governor Newsom legally allowed the term “soil biodegradable” be applied to horticultural mulch films. To ensure the integrity of the product, mulches claiming the “soil biodegradable” label must meet scientific standards for degradability, such as EN 17033:2018 ("Plastics - Biodegradable mulch films for use in agriculture or horticulture - Requirements and test methods"). Equivalent or more stringent standards may also be used in place of EN 17033.

What does this mean for you as a grower in California? It ensures that if you are applying a mulch labeled as “soil biodegradable”, the mulch must meet specific standards of degradability assessed using approved, standardized laboratory tests. This protects the grower from inadvertently applying products that do not meet these standards and accidentally contributing to plastic pollution in soils.

You can learn more about biodegradable mulches at: https://smallfruits.wsu.edu/plastic-mulches/ 

One of the soil biodegradable mulch tests, testing two mulch types, for 2020-21 in Watsonville.

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