How to test your compost (for growth retardants)

compost_cover

Hello there!

I decided to share a simple trick I learned to test commercially available compost (or just any compost that you are not 100% certain about). Why bother testing my compost, you ask? The main culprit would be grass clippings from lawns treated with herbicides (although I am sure there are other ways for a batch of compost to get contaminated). When a lawn (composed of herbicide-resistant grass varieties) is treated, residual amounts of the chemicals are retained in the grass, as well is the soil. These trace amounts may be more than enough to kill or at least stall the growth of non-herbicide-resistant crops*. Unless you are sure of all material that went into the pile to make a certain batch of compost (that is, if the pile is sitting in your backyard), it is a very good idea to test it.

Here is my method (and it’s free!):

  1. Take a look (and a sniff). A good batch of compost should look like very dark (brown-to-black) soil and smell like soil (no foul or funny smells). It should also have a certain texture, once again, resembling rich, fluffy soil.

    merge
    My two test subjects: compost from The Dirt Factory (wonderful place, but had to close this spring, hopefully, temporarily) on the left, and Harvest Mushroom Compost on the right.
  2. The grow test.
    1. Choose some seeds: beans are a great choice, because they sprout so fast, and they are very sensitive to herbicides, so you will be able to detect even low traces of growth-retardant residues.
    2. Fill the pots with your compost and sow the seeds.day1
    3. Wait for the seeds to sprout.
  3. Get your answer! In my case, both kinds of compost performed well, with the seeds growing a bit faster in the mushroom compost.

    day12.jpg
    And the winner is…

Hope you find this useful!

Tatiana

 

References:

*https://extension.psu.edu/persistence-of-herbicides-in-soil

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