Keep your garden safe - bark mulch can be toxic

All Creatures Exchange Article
By: Gail T. Fisher

I recently got an email from a friend with the subject line “Mulch Toxic to Dogs”. I’m always suspicious of emails like this. My first thought is that it’s one of those made-up scary rumors that spread like wildfire across the Internet. There was the Swiffer WetJet scare claiming it contained antifreeze – false; or that several pets have died when their owners sprayed the furniture with Febreze – also false.

These anonymously written and widely spread stories sound plausible enough to be real, but are actually the invention of people with far too much time on their hands – or perhaps a grudge against a manufacturer? But this email was different. It included a link to the website I visit whenever I get one of these scary emails:, the urban legends website that separates rumor from truth. So I checked it out.

It is pretty much common knowledge (at least we hope it’s commonly known) that chocolate is bad for pets, and that consuming chocolate can be fatal to a dog or cat. Whoever would have thought, however, that some bark mulch would contain even more theobromine – the toxic element – than dark chocolate (my dear and good friend).
Here’s what is on the Snopes website (the full link is

“This warning began appearing in our inbox in May 2003. Unlike the majority of scary alerts spread through the Internet there is a good deal of truth to this one, although we've so far been unable to substantiate the claim that ‘Several deaths already occurred in the last 2-3 weeks.’”

This page contains further information from the ASPCA: “Cocoa beans contain the stimulants caffeine and theobromine. Dogs are highly sensitive to these chemicals, called methylxanthines. In dogs, low doses of methylxanthine can cause mild gastrointestinal upset (vomiting, diarrhea, and/or abdominal pain); higher doses can cause rapid heart rate, muscle tremors, seizures, and death.)

“Eaten by a 50-pound dog, about 2 ounces of cocoa bean mulch may cause gastrointestinal upset; about 4.5 ounces, increased heart rate; about 5.3 ounces, seizures; and over 9 ounces, death. (In contrast, a 50-pound dog can eat up to about 7.5 ounces of milk chocolate without gastrointestinal upset and up to about a pound of milk chocolate without increased heart rate.)

“According to tables we've examined, cocoa mulch contains 300-1200 mg. of theobromine per ounce, making cocoa mulch one of the strongest concentrations of theobromine your pet will encounter in any chocolate product. Yet the question of the gravity of the risk presented by this type of gardening mulch remains a matter of debate. According to Hershey's, "It is true that studies have shown that 50% of the dogs that eat Cocoa Mulch can suffer physical harm to a variety of degrees (depending on each individual dog). However, 98% of all dogs won't eat it."

While this may sound like a reassuring statistic, it becomes 100% if your dog is one of the 2% that will eat bark mulch. The danger is especially high for puppies, who will pick up and eat virtually anything within their reach. Rather than take the risk, choose another type of mulch, and supervise your dog, stopping him from munching mulch if you walk him off your property.

It isn’t just cocoa mulch that poses a danger to your pet, it’s chocolate. The darker the chocolate, the more theobromine it contains. Milk chocolate contains between 44-60 mg. per ounce, while unsweetened baking chocolate contains 450 mg per ounce.
The lethal dosage of theobromine is between 250 and 500 mgs per kilogram of body weight. For those of us who aren’t metric-minded, that’s between two-thirds to one and a third ounces for every 2.2 pounds of weight.

If you suspect your dog may have consumed chocolate in any form contact your veterinarian or animal emergency clinic immediately, or the National Animal Poison Information center at the University of Illinois in Urbana. They have computer-supported telephone consultations and a website, as well as a toll free number (888) 426-4435.

Time is of the essence. Again, from the ASPCA: “Theobromine affects the heart, central nervous system, and kidneys, causing nausea and vomiting, restlessness, diarrhea, muscle tremors, and increased urination. Cardiac arrhythmia and seizures are symptoms of more advanced poisoning. Other than induced vomiting, vets have no treatment or antidote for theobromine poisoning. Death can occur in 12 to 24 hours.”

It’s our responsibility to keep our pets’ environment as safe as possible. Avoid dangerous products, keep harmful substances safely away from your pet, and supervise them when you’re away from home. You never know what hidden dangers exist in something as seemingly harmful as bark mulch.

Copyright © Gail T. Fisher, 2007. All rights reserved.
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