Rubber mulch is the byproduct of shredded, used tires. Rubber mulches are touted as suitable soil amendments that do not rot away over time like wood mulches, improve soil compaction and do not feed insects that may live in the garden. The reality is that rubber mulch may not be the best choice for your lawn.
Rubber mulch does eventually break down in soils, being eaten away by microbes, like other organic material. According to Washington State University, some microbe activity is deterred by additives in the tire rubber that leach and kill microorganisms, although some fungi, such as white and brown-rot, will neutralize the additives. The effect additives have on microorganisms raises concerns that some of these additives are toxic.
Nature's Way Resources points to a study at Bucknell University which states that leachate from rubber tires can kill entire aquatic communities and cause health problems in low quantities. Chemicals used in tire production such as cadmium, chromium, aluminum, copper, iron, manganese, molybdenum, selenium, sulfur and zinc may cause toxicity to plants in the soil.
Protecting Against Weeds
Rubber mulches are not proven to be more effective in controlling weeds than wood chips, and are actually less effective, notes Washington State University. Sawdust brings better nutrients and ground cover than rubber can, due to rubber mulch's large size.
Cost and design
Rubber mulch costs more than other mulching materials, such as native mulch or compost, according to Nature's Way Resources. Rubber mulch is available in an array of colors, which allows you to complement flower and plant color in your gardens.
Do not use rubber mulches in yard or landscapes where fire is possible, as rubber mulch is more likely to light and stay lit, making it dangerous, warns Washington State University. The sun's heat may also bring the temperature of black rubber mulch up to temperatures around 172 degrees F. Thin layers of rubber mulch may prove too hot for a regular garden, increasing costs.