Many homeowners use cocoa bean shells, a byproduct of chocolate production, as a landscaping mulch. They like its rich brown color and biodegradability. They also appreciate its chocolate aroma—and so do some pets. Dogs, particularly, may be attracted by the smell and eagerly consume the mulch.

“Some dogs will eat large quantities of fresh mulch, which can lead to intestinal upset,” notes Dr. Steven Hansen, a veterinary toxicologist with the American Society for the Prevention of Cruelty to Animals (ASPCA) “If the amount is high enough, it can lead to increased heart rates and trembling.” Dogs metabolize methylxanthine compounds slowly, so symptoms may take hours or days to manifest. Hansen says death is “very unlikely with current products, because the residual theobromine is very low.”

The ASPCA calls for caution. Cocoa mulch contains caffeine and theobromine, methylxanthine compounds to which dogs and cats are particularly sensitive.

In 2003, the ASPCA investigated cocoa mulch ingestion in 16 dogs. Their study, still posted on their website, reported vomiting in 50 percent of the cases; tremors in 33 percent (with “large or significant” amounts of mulch ingested); tachycardia (rapid heart rate); and hyperactivity or diarrhea in 17 percent of the cases, but no clinical signs of illness in 33 percent of the dogs. Cats can also be sickened from ingesting the mulch, but are less likely to eat it.

The ASPCA notes that the organization “has not received any cases involving animal deaths due to cocoa mulch ingestion.” The ASPCA’s bottom-line advice: Avoid using cocoa mulch anywhere unsupervised dogs roam, and don’t let a dog eat any mulch while out on a leash.

If you suspect a pet has eaten any toxic substance, immediately contact a veterinarian or the ASPCA’s Animal Poison Control Center at 888-426-4435. View the ASPCA cocoa mulch study at ASPCA.org.