How to Test Your Compost for Pesticide & Herbicide Contamination

Here’s a simple test for making sure compost, manure, or other materials are safe to use in your garden and free from contamination with persistent herbicides…

One concern that organic gardeners face when gathering compost or mulch materials is making sure they are free from contamination with pesticides or herbicides. Unfortunately, unless you are buying something that is marked organic, it is difficult to know what’s really in it.

Purchasing organic compost to supply a large garden is cost prohibitive for most people, so many organic gardeners choose to make their own compost using locally available materials such as free hay, straw, horse manure, or other resources they may have access to through friends or neighbors. Unless you know for sure that your source is free from contaminants, you could be poisoning your garden unknowingly, and you can find many horror stories on the internet of gardeners who have done just that.

Tomatoes and many other vegetables are very sensitive to herbicide contamination, and they may show signs such as curled or cupped leaves, distorted stems and fruits, wilting, or even plant death.

Fortunately, there is an easy way to test your compost and other materials for herbicide contamination before using these materials in your garden.

Here’s a simple test to perform whenever you obtain compost, straw, or manure that you wish to use in the garden:

For compost testing

Set up seedling pots or flats and fill half of them with a sterile peat moss-based potting soil… Fill the other half of the containers with a mixture of two parts of the compost you want to test and one part potting soil. Be sure to label for clear identification.

Plant the containers with any legume, but peanuts are best. If certain persistent herbicides are present, germination will be poor and seedlings that do grow will show curled leaf edges. If a peanut plant is used, the leaves will almost instantly fold up.

For manure testing

Plant seedling pots or flats with peas, beans or peanuts (the best choice) and let them grow for a couple of weeks. Mix a slurry of equal parts manure and water in a 5-gallon bucket or other container and let it sit for about an hour. Water half of the seedlings with the manure water and use just water on the other seedlings. If the manure is contaminated, symptoms will appear within a few days.

For mulch or hay testing

Use the same procedure as with manure testing, but soak the mulch, hay or other materials overnight before draining off the water for applying it to the seedlings.



Rose S.

An avid gardener since childhood, I love sharing my passion for gardening with others! I have gardened in a number of different climates and settings, from large fenced garden plots, to tiny patio and container gardens, and I firmly believe that everyone can learn to grow at least some of their own food - no matter where you live. Growing your own food can help you take control of your own health and food supply, and there has never been a better time to get started!

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