It's mulching season, and this landscaping essential just can't catch a break. First came a Web-based rumor in spring 2006 that termite-infested mulch was being shipped out of the Hurricane Katrina-affected zone and into flower beds across America. That alert proved bogus.

Next to circulate was a fear-inducing e-mail alerting pet owners to the fact that fragrant cocoa mulch can kill dogs that eat it. But there is truth to the claim, according to the American Society for the Prevention of Cruelty to Animals (ASPCA). Some dogs are attracted by the mulch's chocolate aroma, and according to a warning from the ASPCA in 2003, "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."

Cocoa mulch is made from crushed cacao shells, which contain caffeine and theobromine, two compounds to which dogs are particularly sensitive. (These substances are also present in everyday comestibles like baker's chocolate, chocolate bars and candies, colas, and tea.) Depending on the size of the dog and the amount of cocoa mulch it ingests, symptoms can range from stomach upset to cardiac arrest. Dogs metabolize the compounds slowly, so symptoms may take hours or even days to manifest themselves. The ASPCA's advice: Avoid using cocoa mulch anywhere unsupervised dogs roam.

Other natural alternatives to cocoa mulch, like cedar chips and pine straw, are typically less toxic but still may contain resins and oils that trigger gastrointestinal disorders in pets that ingest them. And all mulches, including those made from recycled plastics (see our report, available to subscribers), pose a choking hazard, especially in pooches with less-than-discriminating palates.

If you suspect your dog has eaten cocoa mulch or any other toxic substance, immediately contact your veterinarian or the ASPCA's Animal Poison Control Center at 888-426-4435. The center, open 24/7 every day of the year, charges $55 per consultation.