Compost FAQ's

Memorial Day weekend is a popular time for Vermonters to work in their gardens (although this year, the weather forecast might present a challenge). As we enter the weekend, the Vermont Agency of Agriculture wanted to address some frequently asked questions regarding compost.

Compost and Herbicides

During the summer of 2012 some gardeners noticed damage to garden plants that was consistent with herbicide exposure. The Agency of Agriculture initiated an effort to determine if herbicides were involved with the damage and if so, which herbicides specifically might be to blame. After collecting numerous samples of plants, soils and compost and compost ingredients for analysis it was determined that compost with trace amounts of herbicide was causing damage to garden plants. Further analysis has determined that two specific herbicides are detectable in compost; aminopyralid and clopyralid. While both herbicides were present at low levels it is believed that aminopyralid is likely the herbicide causing damage as the cloypyralid detections were below levels generally believed to cause plant damage (10 parts per billion).

The Agency has determined that the herbicides were not present in the compost due to any illegal herbicide use and were most likely the result of the legal use of herbicide products both within and outside the state. As we enter a new gardening season the Agency of Agriculture felt it important to provide information as to the current status of compost and what consumers should be considering when planning their compost purchases this year.

Questions about compost for 2013:

Q: Where do the herbicides come from?

Herbicide residuals can come from a number of sources. Herbicide residuals that cause issues in compost most often come from treated pasture or hay fields, small grains, potentially from grass clippings from treated lawns and food scraps. These herbicides pass directly through animals that are fed treated feeds and end up in the animal wastes that often make up a large portion of commercial compost.

Q: Will there be herbicides in compost I purchase this year?

There could be some low level of herbicide residue in any commercial compost purchased in Vermont, or elsewhere, from time to time. These herbicide residues do not generally cause plant damage at the levels found in most compost products. 


Q: Is compost I purchase this year safe to use?

Compost is safe to use in most instances as herbicide levels are very low.


Q: Will vegetables grown in compost this year be safe to eat?



Q: How can I tell if there are herbicides in my compost?

The best method of testing compost for herbicide residues is to perform a bioassay test.  A bioassay test is simply germinating seed and growing out sensitive plants such as tomatoes, beans or peas.  If there are no symptoms of damage such as twisted, cupped or misshapen leaves and stems then there are not damaging levels of herbicide in the compost.

Q: What can I do to be sure that compost I purchase is ok?

Talking to your compost supplier is the best way to ensure that the compost you purchase does not cause damage to your plants. Many compost suppliers perform bioassays on sensitive species of plants to ensure that their compost will not be harmful.


Q: Can I compost my lawn grass clippings if they have been treated with herbicides?

Yes.  Lawn grass clippings treated with clopyralid may be collected and composted on the site they came from though it is advisable to not use the composted clippings around sensitive plants or in the garden.  The best method for managing clopyralid treated lawn grass clippings is to leave them on the lawn.  This is also the best practice for overall lawn health.  Grass clippings treated with clopyralid (Confront) cannot be collected and sent off site for composting.  In addition, your lawncare provider is required to provide you information on the herbicides used on your lawn including the product name and label safety precautions.  These precautions would include restrictions on the disposal of lawn clippings.  If you do not know what products have been applied to your lawn by a commercial lawncare provider you should ask them.  Clopyralid products are not available for use by the general public.


Q: What is the Agency doing to address herbicides showing up in compost?

The Agency is instituting policies to further restrict the use of the specific herbicides involved.  Clopyralid and aminopyralid products will be designated as ‘Restricted Use Pesticides’ and as such will only be available to certified pesticide applicators.  In addition, the manufacturer of aminopyralid products has discontinued distribution of the herbicide in Vermont for uses on hay or pasture.  The Agency believes that aminopyralid is the herbicide responsible for plant damage last year.  The Agency will also be tracking records of sales and use of these products to determine if more restrictive actions are necessary in the future. 


Q: What about compost produced out of state?

The information pertaining to compost in Vermont also applies to compost from elsewhere.  It is prudent to ask where the compost has come from and if bioassay tests have been performed to demonstrate that it is safe to use.

Q: Who should I call with questions about my compost?

The best source of information about your compost would be from the producer or supplier of the compost.

Q: I used compost in my garden last year, will it be ok?

Yes.  Herbicide residues are broken down when exposed to light and soil microbes.