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How Can We Be Sure That Our Composts Are Safe?

March 15, 2018

When we use compost on our vegetables, we rely on them to be pathogen free. We can’t take the risk of transferring pathogens such as E.coli and fecal coliform from our compost onto our vegetables.

Many organic vegetable and fruit growers rely on manure and compost as a supply of nutrients for their crops.

There are rules with using manure, including a period of time required between application of the manure and harvesting the crop, particularly for vegetables. Manure contains potential pathogens, and it is considered that these pathogens will die within a certain time.

For composts, achieving high temperatures is considered enough to kill potential pathogens. However, some composts, even though they have met the temperatures required for pathogen kill, should be treated like raw manures. This is because when they cool, or when they become wetter, the potential pathogens regrow.

Immature composts are more likely to be at risk for potential regrowth of pathogens.

We have been working on a protocol or guidelines to help ensure that our composts are safe.

The City of Whitehorse produces an OMRI Listed compost from their residential organics program. They wanted guidelines on how to ensure the safety of the compost that they sell. We did extensive testing and found that there was no potential regrowth of pathogens with their marketed product. Based on this, we propose the following protocol to ensure that our composts are safe:

  1. Cure the compost to achieve a maturity rating of < 2 g CO2-C per gram of organic matter
  2. Perform a potential regrowth test that involves taking some of the compost, wetting it to 50-60% moisture and leaving it in a container for 24-48 hours, before taking a sample
  3. Have the sample analyzed for E.coli as well as for fecal coliform as it is a better indicator of potential pathogens.

We are currently testing this protocol ourselves, and what we found surprised us! E. coli does regrow in marketed finished compost here in British Columbia!

I’ve heard the comment before – my compost does not contain biosolids or animal manure, therefore pathogens are not a concern. Sadly, information in the literature years ago already, and our experience today indicates that the purchase of residential organic waste compost may be just as likely to result in regrowth of high levels of E. coli and fecal coliform.

We need to work together, to protect the integrity of the composting industry, to protect the livelihoods of our organic growers, and the health of all of us!

We’d love to get your feedback on how we may be able to improve the protocol so that we can clearly demonstrate that our compost products are safe!

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