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Contaminated Compost

By May 16, 2010

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If you purchase compost, either in bulk or in bags at the home center, you may be unknowingly poisoning your garden. Mother Earth News has reported that the herbicides clopyralid and aminopyralid have been found in compost. The problem is that these herbicides tend to either inhibit germination or cause weak, sickly growth if the plants do manage to germinate. So you may think you have a pest or disease problem, when in reality, it was the compost that you purchased with the hopes of making your garden soil even healthier.

Besides having a poor affect on plant health, the two herbicides in question can persist in soils for years after they are applied. Testing of commercial compost for clopyralid and aminopyralid is not required, and most commercial producers don't bother with it because the tests are costly. When producers have taken the time to do some testing and investigation, they've found that these herbicides are present on everything from grass clippings to horse manure or mushroom compost.

So, if you've been noticing that your plants are just not growing the way they should be, or you're having issues with poor germination, your compost may be to blame. There is a simple test to figure out if compost is the culprit:

  1. Get six four-inch seedling pots, good organic potting soil, the compost in question, and some peas or beans.
  2. Fill three of the pots with the organic potting soil and three with the compost.
  3. Plant a pea or bean in each pot, keeping track of which pots have the potting soil and which have the compost.
  4. Observe your pots. When do the seeds germinate? Are the ones in potting soil germinating faster? Are the ones in compost not germinating at all? If they all germinate, do the seedlings look different? Seedlings growing in pyralid herbicides will have a yellowish color and curled edges.

If you find that you have some of this contaminated compost, you should contact your local extension service to alert them to the problem, being sure to tell them the brand and where it was purchased so they can alert other gardeners in your area. You'll also want to contact the manufacturer. Mother Earth News also recommends contacting the Environmental Protection Agency, as well as your senators, to push for stricter regulations on these herbicides.


June 9, 2010 at 1:25 pm
(1) redmater says:

legumes are damaged/killed at 200 parts per billion BUT tomatoes are knocked off at 3 parts per billion. Thus this test devised to alert the gardener/vegie producer that something foul is in the muck does not provide sensitive enough information to protect members of the nightshade family (maters, taters, tobacco). Such a shame this stuff has been re-released given it’s persistent destructive characteristics.

July 13, 2012 at 7:10 am
(2) D Newton says:

To protect your garden, you should always treat it with activated charcoal (carbon) to detoxify it. It’s inexpensive, easy to use, and will work equally well in soil, manure, mulch, etc. Howard Garrett, the “Dirt Doctor” also recommends activated charcoal on his national organic gardening show, and it is effective on pesticides and other toxins as well. I have seen it sold on Amazon listed as “soil detox”.

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