Compost Mulching Organic Gardening Pesticides and/or Herbicides Residual Herbicides

How to Test for the Presence of Herbicides

The following information was taken from

It is explained in even more detail at

There are many university sites and other sites that have the same information.

Herbicidal symptoms on plants sensitive to the herbicide

  • Slight damage – leaves of new growth are somewhat cupped. Leaves do not lie flat before opening.
  • Moderate damage – leaves are obviously cupped.
  • Severe damange – Most leaves are cupped.  Stems are twisted.
  • <Note from Theresa: In most cases, growth of the plant will be stunted.>

Home testing for herbicides in Compost or Manure

Some laboratories can test for the presence of these herbicides, but the tests are expensive and not as sensitive as a plant bioassay that you can perform yourself. This simple pot bioassay involves growing beans or peas, which are very sensitive to the presence of these herbicides, in the manure or compost.

  • First, take a number of random, representative samples (small shovelfuls) from throughout the pile of manure or compost, being sure to get deep inside the pile. Mix thoroughly. If there are separate sources of manure or compost, conduct individual assays for each.
  • Prepare 3 to 6 small (4- to 5-inch) pots with a 2:1 mix of the manure or compost and a commercial potting mix with fertilizer.
  • Fill several control pots with only the commercial potting mix.
  • Put saucers underneath each pot, or position the pots far enough apart so that water running out of the bottom of the pots will not reach another pot.
  • Plant three pea or bean seeds in each pot, water, and let them grow for two to three weeks, until there are three sets of true leaves.
  • If the peas or beans in the control pots grow normally and the ones in the pots with manure or compost do not, you can assume the manure or compost is contaminated with an herbicide which will adversely affect sensitive plants.

If they all grow normally, it would be reasonable to assume that the manure or compost is fine.

Keep in mind, however, that the test will be only as good as the samples you take. It would be better to err on the side of too many samples than too few (at least 20 per pile).

Home Test for Herbicides in Hay, Straw, or grass clippings

You can create a similar test to the one given above for hay or grass clippings by filling the pot with commercial potting mix only and spreading a thick layer of the hay, straw or grass clippings on top.

This bioassay is explained in detail on the Washington State University Web site:

To Test a Field or Garden:

If a field or garden site has previously been treated with one of the herbicides of concern or been contaminated through the application of treated manure, compost, hay, or grass clippings, a field bioassay can be conducted.

  • Plant peas or beans in short rows scattered throughout the affected area.
  • If herbicidal symptoms appear, do not plant sensitive plants; plant grasses.
  • Test again the following year. If the test plants grow normally, it should be safe to grow broadleaf crops.

For a complete copy of this paper, go to  (Note from Theresa: I included this URL because it was included with the information from the sites I noted above.  But when I visited the North Carolina University site — I could not find this information.)

1 Comment

  • That is a great idea. It’s too bad it’s not as quick an easy as a a pH test using vinegar or baking soda, but at least it can give an idea of whether or not herbicides are there. Now if we could just find a good way to do a home test for pesticides…

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