01/25/2025
Bulking agents are essential for successful composting.
They create air pockets to help oxygen-loving bacteria thrive, absorb excess moisture, and improve the structure of dense, wet material.
Without them, composting can be slow and inefficient.
Now a new study published in Nature.com has identified the best bulking agent for home composting – and it’s both free and readily available.
The scientists focused on home composting because of the vast amount of kitchen waste produced globally.
They noted that home composting is more environmentally friendly than commercial composting, as it generates fewer emissions and eliminates the need for waste transport.
Despite these benefits, kitchen waste is challenging to compost due to its compact structure and high moisture levels.
The Best Bulking Agent
To find the most effective solution, scientists at the University of Lahore tested three commonly used bulking agents: sawdust, fly ash, and fallen leaves.
Their findings revealed that fallen leaves, when chopped or shredded into small pieces (1–3 mm), were the most effective. These leaves composted the fastest, reaching maturity in just 32 days.
The compost made with fallen leaves also had excellent water-holding capacity and drainage.
Germination rates were outstanding, showing the high quality of the compost.
Notably, chili plants grown in this compost were 16.7 cm taller and had more leaves than those grown in compost made with sawdust or fly ash.
By contrast, sawdust and fly ash were less effective.
Using fly ash also resulted in higher salt content, which can harm plants, and both materials slowed the breakdown of kitchen waste and regulated moisture less effectively.
Additional tips for success
The researchers also shared additional tips for composters.
They recommended chopping or shredding kitchen waste into smaller pieces (ideally 1–3 mm) to give microbes more surface area to work on.
They also advised home composters to aerate the compost regularly to maintain oxygen levels and speed up the process.
Takeaways for Composters
Adding layers of bulking material can significantly improve both the speed and quality of your compost—and there’s no need to buy anything.
Fallen leaves are an excellent, free option which can be raked up and put in sacks in the autumn and winter.
Store them in a dry place until you are ready to use them.
For the best results, shred them into smaller pieces. If you don’t have specialised equipment, you can do this by running them over with a lawnmower.
Alternatively, you could follow suggestions made on our Facebook page – put the leaves in a dustbin and use a weed eater to shred them.
If leaves aren’t available, remember that any bulking material is better than none. Materials like straw or shredded cardboard are great alternatives.
You can also use wood chips – if you can, use some which are already partially decomposed, as they will break down more quickly in the compost pile.
Check out our guide to bulking materials for more options.
Related articles
Bulking Agent: The Key to Successful Composting
Researchers Unveil Secrets to Effective Home Composting
Leaf Mold Magic: How to Use Fallen Leaves to Improve Your Garden Soil
Source
Mussa, Sania, et al. “Exploring the Utility of Different Bulking Agents for Speeding Up the Composting Process of Household Kitchen Waste.” Scientific Reports, vol. 15, 2025, Article 2488, https://doi.org/10.1038/s41598-025-85433-0.