When compost goes wrong

Some time ago, a reader reached out to me about a worrying incident: her neighbor’s dog had nearly died after developing mycotoxin poisoning from eating compost. The suspected culprits were sweet corn cobs, having been spread in the garden with the compost while still not fully decomposed. The reader wanted to know if I had heard about this before and, if so, how much of a risk it represented. I thought it might be important to share her concern, and my response, with all of you.

Mycotoxins are poisonous chemical compounds produced by fungus or molds that can appear in food, such as cereals, nuts, spices, dried fruits, apples, and coffee beans, and that can be present even where there is no visible mold. Although it is extremely rare, consumption of mycotoxins can result in acute illness. It follows from there that if food containing mycotoxins ends up in your compost and is then consumed by your dog, there is a chance that your dog may get sick. My reader’s original email smartly outlines symptoms to look for, and what actions to take should you suspect your animal has mycotoxin poisoning:

It is important to note, again, that mycotoxin poisoning is extremely rare—but it can be severe enough that even a vanishingly-small chance of encountering it is worth taking steps to avoid. Here’s what you can do if you have a dog and also love to compost:

1. Dog-proof your compost. This means different things for different dogs. Some will be dissuaded by a simple circle of chicken wire. Others will require more infrastructure to prevent them from access.

2. If you truly cannot dog-proof your compost, avoid composting materials that will have long decay times and are very appealing to dogs—like corn cobs and bread chunks. (I am dog-sitting a corgi right now, and he is a compost monster. He goes right for the bread chunks every time, so I’ve stopped composting them.)

3. Only use finished compost on your home garden. That means there are no visible chunks of food left in it. To be sure, you can even use a length of quarter-inch mesh to sift things before you add.

Prior to hearing from my reader (thank you for writing!), I had truthfully never heard about this being an issue nor encountered it in my work. My own dog has munched plenty of compost in her day and has always been fine, although that certainly doesn’t mean I encourage the habit. The case above is a bit of a gut-check on my “devil-may-care” compost attitude, though, and a reminder that it’s good to know at least a little what you’re doing when you take decay into your own hands. (The neighbor’s dog may not have gotten sick if the neighbors had realized not to use compost containing partially-decomposed corn cobs.)

I’d like to close out with a warm and optimistic reminder that, for whatever pathogen risks to be aware of with compost, the overwhelming reality of any pile is that it’s full of good stuff. Good stuff for you, good stuff for soil, good stuff for the planet. Compost is like a high-functioning immune system and a healthy pile will identify and eliminate most pop-up pathogens entirely on its own. There is also mounting evidence that exposure to healthy soil can dramatically improve and diversify your own microbiome. Like I said, good stuff.

At the end of the day, it’s up to each of us to determine our own threshold for risk and I recognize that for some dog-lovers out there, this may mean they will defer from composting. I respect that choice, although I hope you still do drop off. For me, the good of composting still far outweighs the bad, and I will continue to compost at home—although I now plan to invest in an extra layer of chicken wire to encircle my heap.

Love, Cass