The Hazards of Mulch Processing

Injury

• Landscaping services, municipalities and homeowners may use mobile wood chippers to process tree branches into wood chip mulch. The machines draw the wood in through a feeding mechanism, where hundreds of knives chop it into small pieces. Injuries or fatalities occur when workers are caught into the feeding mechanism or come in contact with the knives. Less frequently, the hopper cover may fly off with great force if improperly used or maintained, causing injury or death. Feed limbs into the chipper blunt-end first and avoid reaching in to push limbs into the machine. Wear cuff-less gloves and pants, work boots and heavy clothing. Keep clothing tucked neatly in and remove any jewelry. Read and follow manufacturer's directions carefully and work with a partner. Keep a phone nearby in the event of an emergency.

Fire Danger

• Rubber mulch, made from recycled tires, is often touted as a safe, permanent alternative to wood chip and other organic mulches. Rubber mulch is actually very flammable and difficult to extinguish. In 1993, stockpiled tires in Virginia caught fire. It took firefighters 9 months to extinguish the blaze. In landscaping settings, rubber mulches are not as effective as organic mulches at reducing weed growth. More importantly, they are known to break down, releasing toxic compounds, such as zinc and lead that may hurt plants, as well as animals and humans. Exposure to rubber mulch can cause skin and eye irritation. Long-term exposure can cause cancer, neurological damage and genetic mutations.

Toxicity

• Organic mulches, such as wood chips, begin decomposing immediately after processing. Like compost, mulches need oxygen to decompose efficiently. When wood mulch is stockpiled in large quantities without aeration, harmful chemicals, such as ammonia and hydrogen sulfide gas can develop. These chemicals are highly acidic and damage or kill plants. When buying mulch in bulk, avoid those that are stored in high piles. Smell the mulch. It should have a fresh, woody smell. Improperly processed mulch smells of silage, rotten eggs or vinegar. If you inadvertently buy mulch that has a foul odor, spread it on a patio or driveway for a day or two. The chemicals will dissipate, making the mulch safe for use on plants.

Pet Dangers

• Most dog owners know that chocolate is toxic to dogs, but even cocoa mulch, a byproduct of chocolate processing, can cause illness when consumed. Cocoa hull mulches contain theobromine, the chemical responsible for illness in dogs. The amount of theobromine present in cocoa mulches vary, and some manufacturers offer pet-safe cocoa mulches. Poisoning is unlikely unless the pet consumes a large amount of mulch, but in large quantities, the mulch may cause vomiting, diarrhea, tremors or even death.