I'm running a leaf compost. It's a pretty big scale. I pick up leafs from all the neighbors chop them with a special purpose tool and then store them for a year in multiple 250 gallon bins. The end result is about 150 gallons of humus per bin after the year after I mix in compost and they decay down. I'll probably do four bins this year, so 600 gallons of humus.

A few neighbors, more concerned about "organic" then me, have raised concerns that because leaves often time get picked up on the ground they may have grass clippings, or worse grass cuttings inside. And that this grass may have been infected with pesticides like Roundup?

Is this a real safety concern? Is there any guidelines on this? I am using the humus in vegetable gardens.

Here is a follow up question about whether or not humus or soil can be tested for toxins and pesticides (rather than just nutritional quality).

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The short answer is Yes, pesticides can be a concern, but that depends on which pesticides you're talking about. And also if you believe what Bayer, the maker of RoundUp, says about the amount of time it stays on leaves. I'll leave RoundUp out of this, because Bayer is pulling it from the US market this year, although I believe it will be available to professionals.

Linda Chalker-Scott, professor emerita at Washington State University, has written about the issue of pesticides in compost - her very short report is in her Horticultural Myths site. I highly recommend that site for excellent science-based horticultural information. In the summary of the linked paper, Dr. Chalker-Scott concludes as follows:

  • The best sources for pesticide-free compost are those that have been analyzed and certified. Home-made compost is also a good choice as long as you are sure your materials are contaminant-free.

  • Unregulated compost can contain pesticides, heavy metals, and other environmental toxins that may be harmful to you and your plants.

  • If you must have your lawn sprayed with persistent, broadleaf herbicides, be sure to use a mulching mower and leave the clippings in place. Do NOT compost them or bag them for clean green removal.

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