Fermentation of grass clippings is an anaerobic process

You are correct in stating that fermentation of grass clippings is an anaerobic process. During anaerobic fermentation, such as silaging or when clippings are ensiled, microbes decompose the organic matter without oxygen, converting complex nutrients into simpler molecules, including organic acids, CO₂, and sometimes methane.libstore.ugent+1

Key effects of anaerobic fermentation on mulch properties:

• Nutrient reduction: Some bioavailable nutrients, particularly easily digestible carbohydrates, sugars, and proteins, are broken down and transformed into forms like volatile fatty acids, alcohols, or gases (e.g., CO₂, CH₄) during fermentation. This means there are fewer rapidly available nutrients left for subsequent aerobic decomposers, making the remaining plant material more resistant to quick decomposition once exposed to air.scijournals.onlinelibrary.wiley+2

• Increased durability: The loss of these easily decomposed nutrients and the concentration of recalcitrant materials (like lignin and cellulose) result in a tougher, more durable mulch blanket. This slows down aerobic decomposition when the mulch is later applied atop soil, prolonging its physical presence as ground cover.biorefine+1

• Mulch stability: This property is valued in mulching—fermented clippings do not break down as quickly as fresh ones, so they provide a longer-lasting protective layer against weeds, evaporation, and temperature fluctuations.biorefine

This is why fermented or ensiled grass clippings make an especially effective and durable mulch: the anaerobic process strips away the most easily consumed nutrients, and what's left is slower for aerobic organisms to decompose, giving you a more lasting mulch effect in gardens or landscape beds.scijournals.onlinelibrary.wiley+2

1. https://www.sciencedirect.com/science/article/abs/pii/S0956053X24002320
2. https://www.biobang.com/web/en/biogas-from-grass-clippings/
3. https://scijournals.onlinelibrary.wiley.com/doi/abs/10.1002/jsfa.6046
4. https://bokashiorganko.com/bokashi-library/bokashi-anaerobic-fermentation
5. https://libstore.ugent.be/fulltxt/RUG01/002/791/211/RUG01-002791211_2019_0001_AC.pdf
6. https://www.biorefine.eu/wp-content/uploads/2021/03/grassification_brochure.pdf
7. https://www.sciencedirect.com/science/article/abs/pii/S0301479718305528
8. https://powerknot.com/2022/03/24/aerobic-composting-vs-anaerobic-composting/
9. https://www.reddit.com/r/composting/comments/1dyv6af/using_fermented_lawn_waste_from_green_bin/