Part 2: What's in Commercial Compost? Nobody Knows

I drove around town for a week with bad-smelling compost.

Yesterday I wrote about how, under the spell of an overwhelming desire for a Japanese maple, I ended up with a truck full of bad-smelling compost. After several days in which the smell did not dissipate, I asked a gardening friend to come by give a second opinion. That was a first – inviting someone over to smell compost. Meanwhile, I put on my former journalist’s hat and made some calls.

The man from the Orange County agriculture cooperative extension immediately put me at ease by 1) not dismissing me as a crank and 2) saying he, too, is “into smelling dirt.” He said he regularly receives calls from people reporting problems with compost. “There’s really no regulation at all on what goes in and what goes out and what’s being sold as compost,” he said. Waste gets moved all over the world these days, and there’s no testing of what’s in it, he said.

The main problems homeowners report are compost infested with weeds – compost is a common way to get Bermuda grass and nut sedge. Sometimes bad compost turns plants brown. “What occurs when piles are not turned as frequently as the should be is they go anaerobic on the inside. It creates a lot of stinky things, which is not only bad to smell but bad for plants,” he said.

I was somewhat relieved when the cooperative extension man said that it’s not common to find outright contaminants in compost. But, then again, since no one’s required to test compost, how are we to know that?

I had become concerned about toxic compost after doing some research online. In 1999, in Washington State reports surfaced of plant damage due to compost contaminated with the herbicide clopyralid. The state later banned the use of clopyralid in products sold to homeowners. And in Britain in 2008, many gardeners reported vegetables withering after applying manure that turned out to have been contaminated by the herbicide aminopyralid. (There are many reports of contaminated compost - too many to summarize here.)

This compost smelled like cigarette butts.
And I wasn't too pleased about the orange mulch, either.

I was surprised to learn that in my home state of North Carolina, in the last three years gardeners and farmers have reported problems with contaminated horse manure that wound up in compost. Farmers frequently spray powerful broad-leafed herbicides on hayfields, and as even a child knows, what goes in must come out. Horses and cows are fed the hay, the manure is collected and then is sold for use in compost. Some of the herbicides remain in the soil even years after the compost is applied, the cooperative extension man said.

Tomatoes are among the plants most sensitive to residues of these herbicides. So are beans. Great. Aside from herbs, tomatoes and beans are my summer vegetable garden.

By then, I wasn’t feeling too happy about all the compost, both bulk and bagged, that I had spread over my garden in the last eight years. Perhaps bagged compost is safer? I asked. “Bags are another mystery product. You never know what you’re going to get,” he said.

I asked for advice. How can be sure I’m buying a product that I feel safe to use in my organic garden? The extension specialist said he does two things when buying compost:

1) Visit the place where you’re buying the compost from and look at the piles. You want to see that the pile has been turned, that it doesn’t have an odor, and that it doesn’t have weeds growing on it.
2) Take a cup of soil from the pile, bring it home and do a bioassay test. Plant radish seeds or grass seeds (something that’s going to germinate in a few days). Wait to see if they come up and when they do, how they grow.

The backyard composter.

“Aside from that, it’s about impossible to determine if you’ve got contaminants in your compost,” he said. I tried to imagine myself, every time I wanted compost, driving an hour and a half to the company that makes most of the compost sold in our area, inspecting the piles, taking a cup of soil, planting seeds and waiting for them to grow. And by the time the seeds were up, wouldn’t a different batch of compost be available for sale?

I made a quick decision. From now on, the only compost that I’m putting on my garden is that from my own pile, where I can control what goes in and know what comes out.

P.S. At the suggestion of my gardening friend, I donated the compost to the gardens of the group home at which I volunteer. I still don’t feel quite right about it, but she said they were  happy to have it.


For information on how herbicides in soil affect tomato plants, click here.

For an excellent overview from North Carolina State University on the problem of herbicide carryover in compost, click here.

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