For your garden, playground or path, you may be considering rubber mulching, made from recycled tires rather than felled trees. It has several advantages beyond saving trees (a great thing), but also some serious negatives—initial cost, chemical leaching, off-gassing, risk of injury and the potential for vandalism among them. Here’s what you need to know to make an informed decision.
What’s Right With Rubber
Rubber mulch is certainly an excellent way to save trees. Because it uses worn-out automobile tires, it also saves significant landfill space. Up to 80 tires are consumed to create one cubic yard of shredded mulch. As a bonus, rubber doesn’t rot or attract termites like wood, giving it a greater lifespan and requiring less maintenance. And in a garden, its non-porous nature allows water to flow freely to the plants that need it, versus wood mulch that tends to absorb some of the liquid.
One of its most popular uses is for playground fill. The US Consumer Product Safety Commission found rubber mulch has the highest shock absorbency of any playground foundation. Certainly, a landing on rubber chunks from a swing ride gone wrong will be less painful than on wood bits.
Despite its ecological, garden-friendly and safety attributes, rubber mulch has its share of detractors because of these serious downsides:
- Initial cost – Rubber mulch is three times as expensive as wood mulch. However, because of rubber’s low maintenance, after just five years it has the cost advantage. How this affects you may depend on if you’re able to make the bigger investment during the time of purchase.
- Leaching zinc – Another consumer concern is the chemical composition of the material and how this will affect plants. Though rubber is water-resistant, it does contain zinc that can leach into soil. Western state soils tend to be starved for zinc, so use there may be beneficial. However, the soil in many Eastern states contains an excess of zinc, and more can harm or kill many varieties of garden plants. Because of zinc’s presence, some scientists recommend rubber mulch for paths and playgrounds, but not for gardens.
- Sharp metal – Metal—used as belting in most modern tires—is not always completely removed during the processing stages. Some companies sell 95% metal-free mulch, leaving the potential for injury to a child on a playground. However, even this concern has a solution: companies like Ground Cush’n offer a 100% metal-free option made from recycled inner tubes rather than tires.
- Flammability – The most serious concern over rubber mulch is its extreme flammability, and the difficulty of extinguishing it once enflamed. In fact, some playgrounds have decided against a using it because vandals have been known to exploit the material’s incendiary characteristics.
- Strong smell and off-gassing – Many children are not distracted enough by their maneuvering on monkey bars and slides to miss the distinctive and unpleasant odor of hot rubber. Adult neighbors of such playgrounds also complain of the stench, particularly during the summer months. And the smell is a good indicator of what scientists have determined: that off-gassing (aka out-gassing) of volatile organic compounds (VOCs) is occurring. In fact, butylated hydroxyanisole, benzothiazole, n-hexadecane and 4-(t-octyl) phenol and two dozen other chemicals of varying toxicity have been detected under normal ambient conditions.
- Poor aesthetics – Many gardeners don’t like the look; after all, chunks of rubber may not exactly provide the ideal backdrop for prized poinsettias and luscious tomatoes.
Ultimately, the decision whether to use natural mulch from trees or rubber mulch from recycled tires will come down to the use you are considering and your personal preferences. Consider the location (garden, path or playground), your long- and short-term budget, the soil (zinc-poor or -rich), safety issues (will there be children around?), risk of flammability through accident or misconduct, your aesthetic and tolerance for the smell on hot days. If you’re considering rubber for creating a path in a cool climate, the product may work fine. But using it in a garden prone to wildfire or even vandals would likely be a mistake.
The Many Merits of Mulching