The choice between using rubber mulch or wood mulch in your garden is not a light decision. Different mulches benefit your soil in different ways and present unique challenges, including possible toxicity, infestation, and the overall cost in terms of both labor and out-of-pocket expense.
Contrary to popular belief, both wood chip mulch and rubber tire mulch can leak toxins into your soil.
Wood mulch products often use dyed woods, old pallets that have been ground up, and other woods that were used in industrial capacities. These woods may contain arsenic and creosote among other byproducts. Unfortunately, because of the reclaimed and used nature of most mulch material, the only way to be sure that your wood mulch is immune to such issues is to use mulch made from tree bark that hasn’t been treated or used for another purpose.
Rubber mulch is made up of shredded tires that have gone out of commission. While the rubber alone can leak zinc into the soil below, the real danger comes from all the other chemicals that come along for the ride. When you consider that this material comes from used tires, it means that any chemicals those tires ever came into contact with could potentially be transferred to your garden.
When it comes to insect infestation, rubber mulch wins the match. Rubber mulch does not attract termites because it is not made of the kind of organic material they like to travel through and settle in. Pests are attracted to the moist, rotting wood in wood mulch. Termites not only use wood mulch to travel, but also to snack on.
If you are worried about a mold infestation, rubber mulch comes out on top again. Rubber tire mulch reduces mold and weed growth by dehydrating most weed seeds and spores before they can reach through to the soil.
Wood mulch, on the other hand, can allow for the infestation of both termites and fungal growth. On top of this, wood mulch can breed "artillery" fungus that can stain nearby cars and homes with fungal spores that, once dried, remain forever.
This depends on the types of benefits you are looking for. Rubber mulch provides excellent drainage for the soil and supplies great insulation against harsh weather. It allows a higher degree of heat to be maintained in the soil, and it better maintains moisture levels.
While wood chip mulch can provide long term benefits to soil as it breaks down over time, it’s also high in carbon. Carbon will seek out nitrogen to help it break down into soil. Nitrogen is a highly beneficial component. Under the right circumstances, wood mulch can actually steal nutritious nitrogen from the plants it’s meant to protect.
Overall Cost Comparison
If you go out to purchase either option, wood mulch is much cheaper on the store shelves when compared with rubber mulches. However, given that rubber mulch lasts longer and does not require yearly re-spreading or repurchasing, its relatively high cost per bag is eventually offset by its longevity. Wood mulch fades, requires repurchasing every one to two years, and can cause termite troubles, which can increase labor and out-of-pocket costs.
While the wood vs. rubber debate endures because these two mulch varieties are very common, there are other options available such as gravel or rock mulch, grass clippings, straw mulch, and many others.