Don't Kill Your Garden With Compost! - Abundant Mini Gardens

Don’t Kill Your Garden With Compost!

Garden soil

Many organic gardeners bring home compost, manure, mulch, and other sources of organic matter to add to our gardens and improve the soil. Unfortunately, there is a significant risk that we may also accidentally introduce a very long-lasting herbicide that is contaminating these materials.

A family of herbicides, including aminopyralid, Clopyralid and picloram, is used to kill broad-leaved weeds. Although it has been banned from lawn-use (where it is still sometimes applied illegally), it is commonly used in pastures and grain fields. This herbicide is absorbed by the plants, and remains in the tissues – even after being dried for hay or used for animal feed.

It can be eaten by animals and then excreted in the manure, where it is still active and strong enough to damage plants. This herbicide is only broken down extremely slowly, and can remain very active even after the original plant tissues or manure has been fully composted. These effects can damage your garden plants for over 2 years after your soil has been contaminated. If the soil is contaminated with high levels of this herbicide, very few garden crops will grow at all.

Unfortunately, lab tests for these products are extremely expensive and not very accurate. The best way to determine if a soil has been contaminated is to try growing plants that are known to be sensitive to these products, and look for damage – primarily cupped leaves, and failure to grow. Especially sensitive plants include tomatoes, eggplants, potatoes, beans, peas, and sunflowers.

Some parts of the country have found up to 80% of the local hay, straw, and animal feed to be contaminated. Even municipal composting programs have been contaminated. Once source of contamination was found to be horse manure from local stables, which was traced to commercial horse feed sold at the local farm supply store. I’m currently concerned about the chicken feed we purchase for our own chickens, and am considering switching to strictly organic feed – though the cost is pretty high.

At this point in time, I personally will NOT introduce any hay, straw, compost, grass cuttings, manure, or similar material without knowing exactly how it was produced, or having it certified organic. I feel fairly comfortable collecting autumn leaves from my neighbor’s yards. Otherwise, I primarily limit my source of organic matter to grass cuttings from my own untreated lawn, or certified organic compost.

I urge all of you to be careful about what you bring home for your garden. This potential problem is not new. Gardeners have been experiencing serious contamination issues for quite a few years now, but there are still many people that have not heard about this issue. I’ve included links below to other articles with more information, including a photo of the typical cupped leaves of damaged plants.

Keep Your Garden Safe From Killer Compost

Use a Simple Compost Test to Avoid Contaminated Materials in Your Garden

Herbicide Contaminants in Purchased Straw, Compost, Manure & Dairy Waste

Be careful out there!



  • Mary Beheler says:

    I had heard that materials from stables can contain high levels of insecticides (used to keep the area clear of flies). I never even thought of herbicides being in hay and such. Thanks

  • Debra says:

    Hi, Steve! I know some skilled gardeners that have had excellent results in adding mushroom compost to their garden, though they also usually added organic fertilizers as needed. BUT mushroom compost may also be contaminated with this herbicide!

    Before I bought a load, I’d pick up a sample of the product, plant some beans in containers, make a tea from this compost, and then water half of the beans (of other very sensitive crops) with this compost tea, and the other half with plain water.

    If the beans watered with the compost tea suffer from curled leaves or other symptoms of herbicide damage, then I wouldn’t use it. (Or you could add the mushroom compost to potting soil, and plant the beans in it, and see if they grow normally.) That’s about the only way to check for contamination. Good luck!

  • Steve Simpkins says:

    I read your article on compost. I can get mushroom compost for about 10 bucks for a pick up truck bed full. I am going to mix it 4 pats compost with some locally mixed potting soil obtained from a nursery. What do you think?

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