Despite being an industry that produces a lot of green, horticulture can be less than earth friendly. Consider the use of non-biodegradable polyethylene (PE) mulch, like that used in berry production.

It gets even trickier for those trying to grow organic. Soil-biodegradable plastic mulches are not permitted as they aren’t made with fully biobased feedstocks. USDA’s National Organic Program lists four main requirements for biodegradable mulch use: Meets one of the established standards for compostability specifications; it achieves 90% in-soil biodegradation; it’s produced without feedstocks or organisms made from excluded methods; and it’s made with 100% bio-based content through ASTM D6866 determination.

That’s a tall order for those attempting to create biodegradable mulch that actually works.

Enter lignocellulosic film (LCF), recently discussed the American Society for Horticultural Science conference by Aidan Williams, an MS student at Washington State University.

She explained LCF is something that’s still being studied – because growers are asking for an alternative to non-biodegradable mulches. LCF is paper-based mulch – and allowed for organic production – but information regarding the performance of LCF as a mulch is lacking.

LCF is made of hemicellulose (different natural sugars); cellulose (a polysaccharide – another sugar); and lignin (a natural aromatic polymer with UV-blocking traits as well as antibacterial and hydrophobic properties). “Lignin is the ‘superhero’ of this trio,” Williams said.

Low-cost, abundant and renewable woody biomass (like sawdust, poplar wood or forest residues) are used to create LCF. The mulch alternative is still in the early stages of experimentation. Some of Williams’s research is exploring how mulch color, lignin use and cellulose manufacturing affects LCF. Her team is also adding a little bit (5%) of biochar to some films, to see how that affects its efficacy.

The team conducted a greenhouse trial growing ‘Cascade Premier’ raspberries from March – June 2024, with mulch treatments placed on the surface of the media and around the base of the plants. They were comparing traditional PE mulch, soil-biodegradable mulch (starch-based, PBAT copolyester), paper mulch, LCF, LCF + biochar, cellulose film and no mulch.

Williams and Co. looked at plant height, above and below ground biomass, introduced weeds and berry node counts – and ended up seeing no significant differences in any category between the different mulches (except the paper-based mulch did lose a fair amount of biomass over the course of the experiment).

There were a couple results to note: Variations in soil temperature were observed, with LCF having the highest reported temperature overall. The cellulose film allowed the most weeds, while LCF did “a comparable job” to suppressing weeds to other treatments (vs. the PE mulch, which saw no weeds).

After the greenhouse growing was done, new mulch samples were then tested to see how they would degrade in soil. Samples were buried in two contrasting climates in Washington State – one warm-summer Mediterranean and the other cold semi-arid.

As expected, the cellulose film was the most degraded and the PE mulch the least. LCF fell in between. After three months, the LCF had degraded by about 50% in both locations. LCF without biochar ended up reaching 99% in-soil degradation within nine months in both environments.

Williams reported that films made with lignocellulose “maintain plant growth relative to PE mulch and biodegrade rapidly once incorporated into the soil” – a promising conclusion for organic growers looking to incorporate it.

That may not be for a while, though. This new mulch alternative is still very new. Williams said a next step will be scaling up lignocellulose material generation so the films may be evaluated in open-field settings and not just greenhouses.

Interested in keeping up with the latest on this research? There’s a website – see lignocellulosicfilm.wordpress.com.