The Finishing Process

After our compost has fully cured—a stage where the material is stable, mature, and cool to the touch—we begin the finishing process.

Why Is Curing Important?

Curing is the final stage of composting where active decomposition slows, heat subsides, and microbial communities stabilize. It ensures the compost is fully mature, safe for plants, and won't rob soil of nitrogen. It’s a vital resting phase that transforms hot, semi-finished compost into a garden-ready product.

Our 5-Step Finishing Process:

  1. Rough Sieving – We pass the compost through a rough screen to remove large chunks, un-composted material, or rocks.

  2. Contaminant Check – We inspect for any missed plastic, wire, or non-organic debris.

  3. Solarization– Finished compost is placed in our solarization container, where temperatures are closely monitored to confirm that the material reaches and maintains a minimum of 104°F for at least three days.

  4. Cooling – Treated compost is allowed to cool before bagging.

  5. Bagging – Once cooled, compost is portioned into individual bags ready for distribution to households.

Each step ensures that the compost you receive is safe, clean, and ready to enrich your garden.

Why We Solarize Our Finished Compost 

At the Greenwich Composting Project, we love rich, living compost — but we also care deeply about safety and consistency. That’s why we take the extra step of solarizing our finished compost before it is distributed to the community.

What Is Solarization?

Solarization is the process of using the sun’s heat to raise the internal temperature of compost in a sealed container. Our finished compost is placed in clear bags inside a custom-built solarization box, where temperatures are closely monitored to confirm that the material reaches and maintains a minimum of 104°F for at least three days. Research from UMass suggests that this temperature threshold is sufficient to kill jumping worm cocoons, while extension guidance on composting more broadly notes that sustained heat also helps reduce weed seeds and pathogens.

Why Do We Do It?

Solarization helps us make sure that the compost we give back to the community is as safe and consistent as possible. This extra step helps reduce the risk of:

  • jumping worm cocoons and other garden pests

  • weed seeds that could sprout later

  • fruit and vegetable seeds that may have survived composting

  • pathogens that could be harmful to plants or people

Especially in a shared community project, this extra step helps protect everyone’s gardens, soil, and crops.

What Happens to Microbes?

Like any heat-treatment method, solarization may reduce some microbial life in the finished compost. Both harmful and beneficial microbes can be affected by sustained heat. However, once the compost is mixed into living soil, it is quickly recolonized by naturally occurring microbes, worms, insects, and other soil organisms.

What About Nutrients?

Solarization does not remove the compost’s value as a soil amendment. Finished compost still provides organic matter and nutrients, while helping improve soil structure, moisture retention, and drainage. In other words, the compost still does the good work your garden needs — we are simply taking an extra step to make sure it is safe to share.

 

Compost Q&A

Q: Does solarization kill the good microbes?
A: Solarization can reduce some microbial life in finished compost because sustained heat affects both harmful and beneficial organisms. However, once the compost is added to soil, it is quickly recolonized by naturally occurring microbes, insects, worms, and other soil life.

Q: Does solarization remove nutrients?
A: No. Solarization does not remove the compost’s value as a soil amendment. The finished compost still contributes organic matter and nutrients, while helping improve soil structure, drainage, and moisture retention.

Q: Why not just skip this step?
A: For a private backyard compost pile, some people may choose not to. But because we distribute compost to many families, we think it is important to take an extra precaution to reduce the risk of weed seeds, pests, pathogens, and anything else that could cause problems in someone’s garden.

Q: Why do you monitor the temperature so carefully?
A: Solarization only works if the compost itself reaches and maintains the target temperature for long enough. That is why we monitor temperatures closely throughout the process rather than simply relying on the weather.

Q: Why does some finished compost smell a little stronger than usual?
A: We have found that some of our finished compost is slightly nitrogen-rich, which can make it smell stronger, especially when stored in sealed bags. This is not a problem once the compost is mixed into soil, but we are working to improve the balance of the finished product by adding more carbon-rich material, such as pine shavings.

Q: Is the compost still safe to use if it smells a bit strong?
A: Yes. A stronger smell does not necessarily mean there is anything wrong with the compost. In our case, it usually reflects the balance of materials in the finished product rather than a safety issue, and it is greatly reduced once the compost is mixed into soil.