Sally Scalera

Brevard County Horticulture Extension Agent
3695 Lake Drive -- Cocoa FL 32926 -- 321-633-1702

Rubber mulch definitely not recommended!

Nov. 11, 2006

Over the last couple of years, I have been asked what I think of shredded tires used as a mulch. The reasons why I don’t like the tire mulch is because the tire mulch is not organic so it doesn’t break down and add organic matter to our sandy soils; and it smells awful when it gets heated by the sun. Research findings from some Universities and state Agriculture Departments are now available and they will hopefully convince people to skip the shredded tire mulch and go back to natural mulches like wood chips or rocks.

Some of the findings that have been uncovered about shredded tire mulch include: it isn’t as good at weed control as wood chips, it is more easily ignited and harder to extinguish, it does break down and can release metals and organic contaminants that are known to adversely effect the environment and possibly human health.

The shredded tire mulches were tested in a number of horticultural production and landscape uses but were found to be less effective in weed control as well as seeding and establishing turfgrasses. Couple that with the fact that tire mulches are also more readily ignited and harder to put out and there are some great reasons for not spreading it around the base of your house! This is even more important for anyone living in wooded areas where there is a potential for wildfires.

Next let’s look at the fact that the rubber mulch does eventually break down. There are many species of bacteria that are known to be capable of using rubber for their energy source and they have been found in a number of different environments, including the water held in the hollow of discarded tires.

There are some additives used when making the tires that can kill these bacteria, but white-rot and brown-rot fungus have been discovered that can detoxify these additives and end up protecting the bacteria. All of this shows that it is a mistake to think of rubber mulch as permanent. This, then leads to the question of what is released into the environment and what does it do once it is there.

Some of the research indicates that the leachate from rubber tires can kill entire aquatic communities of algae, zooplankton, fish and snails. The greatest threat is to freshwater habitats with marine and brackish environments being less sensitive.

Of all of the minerals contained in rubber the most harmful one would be zinc. Some landscape plants are know to absorb too much zinc which results in a toxicity that can lead to the plants death. Back in 1997 an agronomist with the North Carolina Department of Agriculture and Consumer Services studied ground rubber and concluded that it had one critical attribute, high levels of zinc, that could negate all of its other seemingly good qualities. Because of the potential for zinc toxicity it would be best to not use shredded rubber as a mulch or as an amendment in potting media.

Acidic soils and aquatic systems are especially at risk since heavy metals aren’t bound to the soil particles as tightly and are therefore more available for plant uptake. In addition to the zinc, there are other things lurking in rubber like arsenic, cadmium, nickel and lead that can affect the safety of groundwater.

So, when it comes to using shredded tire mulch in the landscape there is really nothing positive to say, but a whole lot of negative things. Hopefully, none of you reading this article have invested a lot of money in rubber mulch and maybe some of you are still in the planning stage. So, save your money and put it to better use, like pine bark nuggets maybe.