Killer compost

This is a story about our gardening group’s painful encounter with the damaging downstream effects of persistent herbicide use. It’s a long and sometimes depressing report, but we think it’s important to document this frustrating problem and share what we have learned. We hope this information will be useful to other gardeners. As we learn more, we will post updates.


Compost is a highly valued (almost magical) soil amendment that is for most organic gardeners an essential part of a healthy gardening program. It provides a diverse mix of microorganisms and nutrients that encourage healthy plant growth. It increases soil’s water holding capacity. And it improves soil tilth, which results in better aeration for germinating seeds and root development. 

But let just a tiny pinch of a persistent herbicide sneak into that compost, and suddenly your favorite soil amendment becomes a garden terminator. 

That’s what happened to Green Corn Project earlier this year. In May, we noticed that tomatoes and eggplants in many of our Spring gardens were looking very wrong. New leaf growth on previously healthy transplants was oddly shaped – elongated, twisted, curled and cupped. Overall growth was stunted. And there was almost no fruit production.  After a lot of detective work, including bean tests (bioassays) and many conversations with our compost supplier, horticultural experts, agriculture officials and fellow gardeners, we concluded that some sort of herbicide (probably one of the persistent herbicides) was lurking in the compost and garden soil we were using in our raised beds.

Which means, unfortunately, that dozens of Spring gardens around Austin were impacted.  We’re still taking stock of damages, but it appears that more than 40 garden beds were damaged by bulk soil and compost we purchased in March and early April.

That soil and compost was used for Spring Dig-in events at Title 1 elementary schools, community centers, women’s shelters, individual homes, alternative learning centers and daycare centers. Needless to say, this has been a scary, maddening and costly experience for everyone associated with Green Corn Project and those gardens.  

Note: The compost incident reported here is based on our experience with raised bed gardens that GCP volunteers installed and planted in early Spring 2022. The transplants we grew to sell at our spring fundraiser at Boggy Creek Farm were not affected. We don’t add compost to the seedling mix we use to grow transplants for our spring and fall plant sales.

Where did the contaminated compost and soil come from?

The compost and soil were purchased at GeoGrowers, where GCP has been purchasing bulk products for many years. We respect George Altgelt and have been pleased with his compost and soil prior to this incident. I mention his business by name not to make him the villain in this situation but to illustrate that herbicide contamination can happen unexpectedly to any compost producer, no matter how reputable. And it seems to be happening more and more at compost yards around the country.

Altgeit regularly does bean growing tests of his compost, which contains dairy farm manure, to make sure it doesn’t contain herbicides.  Despite the testing, some sort of plant-killing chemicals managed to get past him and into the Spring gardens of some of his regular customers, including Green Corn Project and Liz Cardinal of Austin Edible Gardens.  

Was the compost tested by a lab?

Yes, it was tested by the Texas Department of Agriculture (TDA) after Cardinal filed a complaint. Vegetable plants in two of her clients’ home gardens showed symptoms of herbicide damage. TDA inspectors took samples of the plants and the soil in the raised beds. Samples were also taken around GeoGrowers’ soil yard. The results came back negative for the chemical they thought they might find – aminopyralid –  a persistent herbicide found in Grazon, a popular weed killer made by Dow Chemical that’s commonly used on pastures and hayfields. (See below for more about how to file an official complaint.)

Were they testing for the wrong chemicals? Maybe. Or maybe by the time of testing, the contaminated materials at the compost yard had been mixed in with other cleaner materials so that the concentration in the samples was too low to show up on a test. Or maybe something was amiss in the testing procedure. It’s hard to know for sure why the test results were negative.

Everyone I talked to who was involved in the investigation agreed that the distortions on Cardinal’s plants looked like herbicide damage, but because nothing was found in the lab test and there were no other formal complaints, no further action was taken.

“We cannot justify moving forward with only one complaint,” says Elizabeth Prokop, a specialist in the pesticide division of TDA who was involved in investigating Cardinal’s complaint. (See below for more about the complications that surround soil testing and lab results.)

Green Corn Project did not file a complaint with TDA. Nor did we do a lab test. But we did do a lot of bean testing (bioassays), which is considered by many agricultural experts to be the best way to test for herbicide residues in soil. We planted bean seeds in 20 4-inch pots filled with soil taken from different raised beds we had planted all over Austin. All the soil in those beds (and the compost in that soil) had come from GeoGrowers. Every test bean we planted grew a deformed plant. We knew we had a big problem.   

Curled and cupped leaves on GCP’s bean test plants. Photo by Brooke Letterle.

What is GeoGrowers saying about this incident?

George Altgeit says he has always been committed to producing toxin free products and will continue to do his best to keep his compost clean. 

“For all of us in this business of gardening, landscaping and agriculture, the misuse of herbicides has become a severe problem, “ he says. “These toxic herbicides that do not break down are making it into animal diets all over the country. This is carelessness on a grand scale in addition to being illegal. Beef, poultry, eggs, milk, and everything made from milk is all being tainted…. It’s not just the home gardens.” 

He recommends that concerned gardeners contact their state officials and ask them to take action to make the food supply cleaner.

He also wants gardeners to know that GeoGrowers offers compost alternatives for those who are seeking ways to improve their soil fertility without using manure.  

What are persistent herbicides?

Persistent broadleaf herbicides (aminopyralid, clopyralid, aminocyclopyrachlor, picloram, fluroxypyr, triclopyr) are found in a number of popular weed control products that have been used by farmers and forage producers since the early 2000s. They’re called ‘persistent’ because they don’t break down easily and can persist in hay, straw, compost and soil for years.  They’re different from herbicides like glyphosate, 2,4-D, and dicamba, which break down much more quickly without leaving long term residuals in the soil. 

When animals eat grass or hay treated with persistent herbicides, the chemicals pass through their systems and are concentrated in their manure.  If that manure is used to make compost, that compost can do serious damage when added to garden soil. As little as 1 part per billion (ppb) of persistent herbicide residues can turn a garden into a no-grow zone for up to 18 months, and sometimes for as long as 3 years, depending on the concentration of the chemicals, the microbial and moisture content of the soil, and the amount of light the garden receives.  One ppb is equivalent to one sheet of toilet paper in a roll that stretches from New York to London. 

Should you eat vegetables grown in soil that contains persistent herbicides?

Vegetable plants grown in soil that contains persistent herbicide-contaminated compost may manage to produce some small fruits. The U.S. Environmental Protection Agency (EPA) says that fruit is safe to eat. (Regardless of what the EPA says, Green Corn is advising its gardeners to err on the side of caution and not eat the leafy plants or fruits grown in an herbicide-contaminated garden bed.)

Edible garden plants that are known to be susceptible to persistent herbicides include carrots, dill, cilantro, fennel, parsley, eggplant, tomatoes, peppers, potatoes, lettuce, strawberries, squash, grapes, spinach, beets, chard, legumes, and mushrooms. Many flowers, including daisies, marigolds, sunflowers and some roses are also susceptible. 

What is Green Corn Project doing about its contaminated garden beds?

As longtime organic gardeners, Green Corn Project’s volunteer board members are accustomed to the challenges of plant-killing weather, critters and insects, but plant-killing compost is a new challenge. We did a lot of research and consulted with other gardeners who have experienced this same problem and then we came up with a remediation plan.  And then we got very busy.  

Volunteers worked all summer to remove damaged plants and soil, at a depth of 3 to 4 inches, from every bed we had added contaminated compost and soil to in April. We threw the plants away (in garbage designated for the landfill) and disposed of the compost and soil by spreading it on grassy areas. (Persistent herbicides are formulated to kill broadleaf plants, but not grasses.) We also added amendments to boost the microbes in each bed to help break down any remaining residues — Happy Frog Soil Conditioner, Archaea and compost tea. And finally, we planted sunflowers. As the sunflower plants grow, they serve as bioaccumulators, as well as herbicide indicators. We figured that if the sunflowers showed signs of herbicide damage, we would know we needed to do more remediation before replanting the beds with vegetables for the fall growing season.

As an extra precaution, two weeks later we revisited the beds and planted beans alongside the sunflower plants. Legumes are very sensitive to herbicides and are excellent indicators of persistent herbicide residues in the soil. So far, many of the beans and sunflowers are looking pretty good, so we’re crossing our fingers that our remediation is helping. 

Unfortunately, at least one of the remediated raised beds has failed the final bean test;  the bean plants in that bed produced severely distorted leaves (see photo below), so we have decided to remove and replace all of the soil in that 4 x 8 bed before planting a fall garden.

New sets of leaves on these test beans are cupped, curled and twisted. Photo by David Huebel.

In short, it’s too soon to say whether all of GCP’s damaged garden beds will be ready for growing fall vegetables, but we’re doing everything we can to make it so.  We’re pretty sure any remaining issues will be resolved by spring 2023.

Herbicide contamination of home gardens is not a new phenomenon. Why does this keep happening? Is anyone trying to solve the problem?

I talked to folks at the TDA and studied reports from the United States Compost Council (USCC), the EPA and Dow Chemical.  They are of course all aware that persistent herbicides are showing up in urban gardens, but no one seems particularly focused on taking action to stop it from happening.  The few controls in place to address the issue – which include product labels, educational reports, herbicide applicator licenses and consumer complaints –  apparently haven’t been enough to prevent persistent herbicides from entering the compost stream and contaminating school gardens, community gardens, and backyard gardens.

The TDA will investigate herbicide contamination issues if it receives a well-documented formal complaint that indicates possible misuse of herbicides (see how to file a complaint below). At that point it may choose to collect plant and soil samples for diagnostic examination and testing. Unfortunately, lab tests on soil samples are notoriously inconclusive because the content of compost and soil piles is constantly changing as materials decompose and are moved around and in and out of the bulk producer’s yard. In addition, upstream suppliers of the compost inputs – manure, grasses, rice hulls, etc – are not routinely included in an investigation unless a specific separate complaint has been filed against those suppliers or unless multiple complaints point to the same supplier. 

According to TDA specialist Prokop, there are about 47,000 licensed pesticide/herbicide applicators in Texas, but only 30 investigators tasked with ensuring that the pesticides and herbicides they’re applying are being used correctly and legally.  (Those licenses are not all related to farming; some are for weed clearing along highways, public park maintenance, etc.) 

She says the best way to reduce herbicide contamination incidents is for gardeners to file a complaint every time they have a problem. “The more complaints we get, the more investigations we can do,” she said. “And the more complaints we have about one source, the more reason we would have to go upstream.” 

Another complicating factor, according to the US Composting Council, is that no government or independent lab in the United States can adequately test for aminopyralid in compost at or below the 1 ppb level. Therefore, many lab tests may be missing it. A negative test result may mean there’s not enough herbicide in the soil sample for the test to measure even though it’s enough to damage vegetable plants.

The USCC, on its website, acknowledges that its members could be testing more rigorously for persistent herbicide contamination before selling their compost, but says the tests are too time-intensive if done in-house and too expensive if sent to a laboratory. So, the USCC has concluded that it is unfair to place the burden of proving the compost is clean on the compost producer. (See the USCC’s  website for more info on the problem from the perspective of compost producers. USCC fact sheets. FAQs, USCC position statement. )

The EPA has been reviewing the persistent herbicides for the last few years, but so far hasn’t done much more than require that new educational reports be created and more cautionary words be added to the product labels.  

An online educational report from a Texas A&M AgriLife Extension expert has cautioned Texas dairy farmers to take care not to use persistent herbicides if they sell grasses or manure off their land to compost suppliers or producers. I couldn’t find any AgriLife reports intended to help Central Texas home gardeners avoid buying the contaminated hay or compost that is being produced and sold despite the product labels and educational reports urging caution.

How do you report a compost or hay issue in Texas?

If you think your garden has been damaged by persistent herbicide residues in compost or hay,  immediately file a complaint with the Texas Department of Agriculture by calling 1-800-TELL-TDA. Save the compost, soil or hay and document the source of your materials and the date they were purchased. Try to find out where your compost producer got their input materials. Also try to keep your sick plants alive so they can be examined and tested. (TDA complaint procedures.)

Is anyone looking out for the interests of home gardeners?

A few university extension programs have published reports on persistent herbicides that include suggestions and photos that are intended help home gardeners understand what they’re up against: 

A quick call to the AgriLife office in Austin resulted in this very practical bit of advice: Make your own compost or buy compost that doesn’t contain manure.

And after a deep dive into this topic, it seems that this is indeed the smartest, most certain, course of action, especially given how challenging it seems to be for the state to track or prevent misuse of persistent herbicides. 

Are scientists studying ways to solve problems resulting from the use (and misuse) of persistent herbicides? 

Yes. But results have been mixed.  Researchers have tested several bioremediation methods involving the use of microbes to transform environmental herbicide components into non-harmful or less harmful molecules. While some of these helpful microorganisms have been isolated, trials of their use in environmental applications have been disappointing. One study in 2020 concluded that using a mix of microbes that show a higher genetic and metabolic diversity may be more efficient than single strains when attempting bioremediation. 

According to several studies, adding organic carbon and/or biochar may improve water holding capacity, microbial numbers and the microbial diversity needed to break down herbicides more quickly. But again, results have been mixed. 

Texas A&M researchers in 2018 reported that activated charcoal shows promise for remediating soil contaminated with persistent herbicide residues. But they noted that vegetable crop response was variable and so application rates of the charcoal may differ for specific herbicides and plant species. 

How common is persistent herbicide contaminated compost?

I haven’t found any official reports on how often persistent herbicide residues have been detected (or reported) in commercial products, compost facilities, hay farms, or dairy farms. Nor are there reports on how many home and community gardens have been seriously damaged. If anyone is keeping tabs, they’re not making that data easy to access. 

However, I have found many social media reports from gardeners all over the country sounding alarms about persistent herbicide residues damaging their gardens. Here’s a small sampling of stories from gardeners:

How can you be sure your garden damage is a result of herbicide residues and not something else?

Nutrient deficiencies, plant diseases and insects can cause symptoms that look similar to herbicide damage. According to extension experts at Oregon State University, you should suspect damage from herbicides when:

  • More than one type of plant is affected.
  • Damage appears on only one part of the plant(s)
  • You’ve ruled out other causes of plant damage. 

This report from Oregon State contains photos and information to help you rule out the other common causes of plant damage. For example: Plant diseases caused by viruses cause stunted growth, distorted leaves and a mosaic pattern. The damage often looks similar to herbicide damage. The difference is that virus diseases usually affect only one kind of plant, such as tomatoes OR grapes. Herbicide injury will affect different kinds of broadleaf plants all at once.

Can you have your soil tested locally for herbicide residues?

Yes, but it’s a complicated process and not cheap.  

If you’ve ruled out other causes of damage and you want to try to nail down exactly what your contaminant is, you can send a sample to a laboratory that does herbicide testing. However, you may need to test several times before you can zero in on the particular herbicide in your soil because you have to tell the lab the exact chemicals you want to test for (which may be a guessing game), and you need a high enough concentration of the chemicals to show up on the test.

Discuss your particular situation with the lab before going through the process to make sure it’s worth your time and money to test.  Most tests cost at least $150, and often more. 

Labs in the Central Texas area that list herbicide testing as one of their services include:

What can you do to avoid herbicide-contaminated compost?

Ideally, if possible, make your own compost so you have control over all inputs. And unless you’re getting manure from your own cows, goats or horses who are consuming herbicide-free feed and grasses, leave manure out of the mix. As an alternative to manure, you could try adding one of the following amendments: 

  • Alfalfa 
  • Blood meal
  • Bone meal
  • Cottonseed meal
  • Fish meal
  • Kelp meal

If you have to purchase compost, ask the seller or the producer about the source of the materials used.  If the compost contains manure, ask if herbicides were used to grow the animals’ feed or grass. Find out if the compost producer does bioassays to test the product before it is offered for sale. If no testing is done, do your own tests before using the product. (Here’s a guide on how to conduct a bioassay.)

If you are obtaining straw or hay for your garden, ask if it came from a site that may have been sprayed with persistent herbicides. 

If you’re collecting lawn grass clippings in your neighborhood, find out first if weed killing  products were being used on the lawn. Weed and feed products usually contain  2,4-D, dicamba, and/or MCPP. Although these herbicides break down much faster than the persistent chemicals used on pastures and hay fields, they can still damage or kill your vegetable plants and may reside in compost for up to 40 days.

It’s also possible that grass clippings from home lawns could contain persistent herbicides, although that would be a violation of approved use of those herbicides.  A tainted compost incident in 2020 that affected many home gardeners and small farmers in North Carolina drew attention because it was suspected that the contamination came from grass clippings from residential lawns that had been illegally sprayed with clopyralid. After being mowed, the contaminated grass clippings were placed in city yard waste canisters that were sent to a local composting facility. (In 2002, DowAgro Sciences “delisted” clopyralid for residential use.)

Clopyralid contaminated compost caused this damage to a home gardener’s tomatoes in North Carolina. This photo was included in public comments the gardener made to the EPA during its re-registration review of the herbicide in 2020.

Is there any way to be certain that the compost you’re purchasing is clean?

No, not really. Testing compost for possible herbicide residues is not currently required by any regulatory agency.  Testing for herbicide is not even a requirement for organic certification, so buying organic products is not a guarantee of an herbicide-free product. Basically, it’s a buyer beware situation.

There are a few voluntary accreditations, including OMRI, NOP-approved, and USCC certification. These accreditations may demonstrate a producer’s commitment to accountability, a relatively clean product, and a clean environment, but unfortunately, they don’t guarantee that the products are herbicide-free.

The main legal restriction that is supposed to control the misuse of persistent herbicides is the label on weed killing products used by farmers and forage growers. Here’s an example from the label of a popular Dow AgroSciences product: “Do not use hay or straw from areas treated with GrazonNext HL within the preceding 18 months, or manure from animals feeding on hay treated with GrazonNext HL, in compost.” And “It is a violation of Federal law to use this product in a manner inconsistent with its labeling.” 

Clearly Dow knows this product has the potential to create a problem if it is allowed to get into forage or other compost ingredients. But it’s also clear that this labeling has not prevented continued misuse of the product. 

How can you get rid of a big pile of contaminated compost?

Take it to a landfill or spread it thinly on top of grassy areas away from water sources.  It will not kill the grass and persistent herbicides will break down into relatively harmless molecules in 1 to 3 years. Meanwhile, do not use trimmings from that grass in your homemade compost. Alternatively, you can try contacting the company that sold you the contaminated compost and request that they come and remove it.

Can you fix contaminated garden soil?

No one has reported a proven, science-based fix for remediating soil that has been contaminated by persistent herbicide residues, other than physically removing and discarding the soil or simply doing nothing for a few years until it breaks down into less harmful particles.   

Avid organic gardeners desperately looking for easier, quicker fixes have been trying all sorts of remedies.  A common remedy is to add microorganisms, keep the affected soil moist and then plant herbicide resistant cover crops to help draw out the toxins. Does this help?  Probably, but results can be slow and inconsistent. Whatever remediation you choose, it’s a good idea to refrain from planting susceptible vegetables or flowers in a contaminated area until a bioassay (bean test) shows that plants will grow normally in the soil. 

For suggestions on different ways to remediate herbicide contaminated gardens, check out these posts: and


This content was researched and written by Austin writer and longtime gardener Renee Studebaker, a retired journalist and a volunteer board member of Green Corn Project