Now You Too Can
Kill Your Garden
With Rubber Mulch!
"Kill the thing you love."
-Oscar Wilde
Ground up rubber tires have been tested as soil amendments & surface mulches, & discovered to kill ornamental plants due to its zinc content; to be a fire hazard dangerous to place near buildings; & to smell incredibly bad.
Often a single application is sufficient to kill plants. Nevertheless, more & more companies are obtaining crumb rubber waste product & packaging it in nicely designed bags that recommend it for gardens. Still other companies slip it into commercial composts as a bulking agent. The excuse for this is that rubber does have a slight (very slight) nitrogen value. But the toxicity from zinc, cadmium, & other heavy metals, more than makes up for any faint chance of a benefit.
Rufus Chaney of the USDA Agricultural Research Service, analysing twenty years of research, concluded that the majority of research leads to the conclusion that for the Zinc factor alone, ground or chipped rubber should never be used in gardens or composts. Yet rubber remains an undisclosed ingredient in some commercially packaged composts, so that even a gardener who knows better than to dump rubber particles all over their garden may be doing so unknowingly.
A gardener needs only consider the zinc factor & the stink factor to realize this is toxic garbage unsuitable for landscaping. But there are other heavy metal & toxic contaminants in crumb rubber, including arsenic, cadmium, lead & nickel, which can effect the safety of groundwater.
The law does not require crumb rubber to be listed as "crumb rubber" when it is used as an ingredient in soil ammendment products; it can be listed as a bulking agent or some other imprecise reference intended to hide from you the fact that you just bought something with ground up rubber tires in it.
As one might suspect, the attempt to find garden uses is inspired not by a desire to improve horticultural & agricultural techniques, but by a desperation to get rid of a type of trash that our culture generates by the billions of tons yearly, & which is difficult to discard. Political & economic pressures have been brought to bare even on horticultural research projects.
One might reasonably ask how ground-up rubber tires ever became legally marketed to dump in our gardens since it is known to kill plants. The sorry fact is, the governmental priority was finding a way to get rid of all those used tires. The thinking runs something like this:
- The foremost waste management problem in America was for decades this: what to do with used tires. One way or another this problem had be taken care of.
- We're an automobile oriented society & whatever the answer to the problem may be, it must foremost be compatible with the requirements of automobile & tire manufacturers.
- If the tire industry were forced to spend money to clean up a problem their own industry causes, said industry would be annoyed & move to Indonesia. For a fee, millions upon millions of used tires have already been accepted in Malaysia & Thailand & the Philippines, enormous mountains of fire hazard waste rubber, & these countries would certainly welcome the manufacturers as well. So the solution must consider the necessity of keeping jobs & profits in America, even if that means polluting our own immediate environment as horrifically as is permitted in third-world countries.
- If the public could only be induced to purchase bags & bags of ground up rubber to disperse on their properties, this would be the ideal solution, for costly clean-up & disposal would be transformed into a source of industry profits rather than expense.
- If the environment is harmed by the Final Solution, the harm has to be weighed against the positives of doing away with the waste while adding profit to industry coffers.
- Yes, this solution creates another environmental hazard. But even bad news can be worded to sound like good news.
Therefore studies are set up specifically to find something good to say about this crud. For a single example of the inevitable response to the outlined factors, we find that the Northeast Recycle Council (NERC) has been fully coopted by the rubber industry, repeatedly recommending crumb rubber products as ecology-positive recycled goodness.
Under pretense of being a watchdog & research non-profit, rather than industry flunkies, NERC has been promoting all kinds of ideas profitable to the likes of the rubber industry. In their own minds they may or may not realize they are sell-outs, dupes, or frauds. The Council may well have convinced itself that the enormous problem of used tire waste must be solved in a profitable manner or it will never be solved at all — & having first duped themselves, it is easier to dupe the public into believing toxic rubber mulch & compost filler is great stuff for everyone's gardens.
Hence when NERC promotes "buy recycled products!" the focus is on the word "Buy!" because profits is what they encourage, even at great expense to public health & well being. Where they recommend you spend your money can easily turn out to be harmful, & the recommended uses for the purchased item entirely inappropriate. But soft-touch ecologists are apt to do exactly as instructed when the word "recycled" is attached to a harmful product.
Rufus Chaney is unambiguous about this: "It may look like good money, but rubber-Zn will ruin the compost product."
The game is stacked against the truth, & some value for this crud is being ballyhooed. The toxic factors are increasingly & intentionally not part of studies; & even if a well-designed study has to admit that these products kill plants, that is shaped even by the researchers themselves to help industrial PR flacks transmogrify a negative finding into the wonderful proof that crumb rubber makes a great weed-suppressing mulch.
Chemical toxic gasses ("volatile organic compounds" & "polycyclic aromatic hydrocarbons") are released from ground up synthetic rubber. These volatile gasses are known to cause irritation of nasal & respiratory passages & can cause central nervous system damage, depression, nausea, dizziness, headaches, dermatitis, eye damage, & kidney damage. The VOCs & PAHs are sufficiently toxic that products with ground rubber should not be used in enclosed areas or indoors, such as indoor horse arenas where they are nevertheless recommended for use by vendors. In enclosed areas these hazards pose a human health hazard as well as to animals.
This nevertheless gets dismissed because nobody was ever asphyxiated to death by these gasses, & really it is mainly a problem of the hideous stench, whether indoors or outdoors, especially on any hot day.
Well hey, if it's mainly only the hideous stench, then all right, no problem!
Industry can "spin" even the most horrendous finding & claim it is a good thing. AlternaMulch brand, like many others, boasts that this stuff won't break down in the environment in a century. (Contrary to widespread belief, rubber does decay when ground up for maximum exposure to funguses & microorganisms, but it does so at a very slow rate, after first leaching toxins into the soil.)
Or, since the unembelished fact is: "Zinc in crumb rubber toxifies soil with as few as one application; & with repeat application, eventually nothing will grow in that soil," smiling industry faces change it to, "The zinc content of rubber mulch & compost filler is beneficial to zinc deficient topsoils!" If the unembellished fact is: "Crumb rubber mulches & bulking agents kill flowers," the Industry version is that it "retards weeds."
It is just amazing how easily horrific facts can be touted as plusses!
The idea of crumb rubber in the garden has been around for 50 or more years & was initially a Cornell University research project seeking ways to use ground up tires for soil amendments. At that time the pressures were insufficient to concoct a complete lie. Since the findings showed conclusively that it was unsafe, very little came of those first field trials, although some use as unlabeled bulking agent did begin.
So the first serious commercial inroads for bags of avowed crumb rubber took decades to take hold. The first successful inroads were made by promoting crumb rubber as a playground mulch, on the premise that children who fell off playsets would bounce on the ground & be perfectly safe. With this use, the problem of the rubber killing ornamental plants could be ignored, even though playground rubber inevitably migrates into surrounding park gardens & lawns.
But even in landscapes without plants to be killed, rubber mulch presents an extreme hazard on playgrounds. Field tests overseen by Larry Stewart at the Ohio State University Agricultural Technical Institute discovered rubber mulch to be a considerable fire hazard. This study compared many mulching materials & discovered: "All of the materials tested were different in their ease of ignition. Some, like cocoa hulls, never ignited under any of the circumstances, while others, like ground rubber, had flames within a minute & were a struggle to extinguish. It's rare that you would have a fire in mulch that is immediat. Most creep along under the mulch & then ignite, with rubber as an exception--it spreads fast and can't be contained. What's scary is that rubber's commonly used in playgrounds." A single flicked cigarette butt could be sufficient to turn a landscape or child's playground.
Many of the numerous companies in this relatively new industry of selling rubber particles as mulch cite (as vaguely as they dare) a Pennsylvania State University study as though it lauded the product. But that study made no evaluation of the effects (good or bad) on gardens; it merely showed that if you fall down on rubber it hurts less than if you fall down on sticks or concrete or rocks. Well duh.
Playground use of rubber mulch was never as safe as vendors pretend, even if only the fire hazard is weighed. But the reality has been that several researchers are concerned with the potential dermatological injury from contact with chemical components of ground rubber, which is a major health-hazard in the rubber manufacturing industry & likely to be a cause of dermatitis in children who fall & run & play in granulated rubber, which should not be touched except with Playtex or nitrile gloves.
Despite the fire harzard that makes crumb rubber inappropriate even for playgrounds, nevertheless playground use was the foot-in-the-door that soon led to broader & broader recommendations for gardening options, with the zinc & heavy metals issue conveniently mislaid.
Rubber Resources of Florida under the brand name Everlast (great name — admits you can never get this crud back out of the environment), & by YardCo (also of Florida) are just two examples of packagers who hope you'll be stupid enough to poison your landscape with their low-investment high-profit waste product. The product, they will imply, has been thoroughly tested (by themselves). A test garden in Hudson Florida called Garden World Nursery is owned by Rubber Resources & amounts to mere Display Propaganda posing as a study. Of course they're not actually claiming on their product label that rubber mulch has any actual value except for covering up the soil, so they're not quite lying about anything. But the clear implication, by showing the product strewn all around plants, is that it is recommendable to do just that.
There's in particular an ongoing propagandistic attempt to convince organic gardeners that by participating in recycling of this kind, we are good liberal nice people doing our part to save the world. But for the average gardener who puts poisons on their garden all the time anyway, that market is already sewn up.
YardCo promises their cedar-colored rubber particles are "95% steel free!" Most such products are mum on the topic of steel content, & don't even make the laughable boast that their product is 5% metal particles. Bits of radial tire steel in the garden is obviously a negative factor. As much as possible, the steel that is in used tires is removed to recycle into new steel products, as steel is the only legitimately recylcable component of tires. Once the majority of the steel is removed, what remains is toxic waste that most certainly shouldn't be used in landscaping. The rubber itself cannot be recycled into new rubber, which is why novel & dangerous uses have been concocted.
For every 5,000 pounds of tires recycled, about 2,000 pounds of steel is recovered first, & another 2,000 pounds of shredded rubber goes to the "rubber mulch" industry. The remaining 1,000 pounds is primarily the rubber-to-steel bonding agent. Most of that goes to landfill though a very small amount goes to the manufacture of tiles & architectural molding. It has many of the same environmental problems as are outlined in the companion essay on Deadly Polymers in the Garden. So a percentage of harmful steel, & another percentage harmful bonding agent, does remain in the shredded rubber when sold for gardening purposes.
One brand of rubber mulch claims to have no steel at all, but nothing requires them to prove it, & the companies that sell this stuff are mainly just buyers on the open market for pulverized rubber left over from higher in the recycling pecking order. None of the companies even mention the lingering percentage of latex or urethane bonding agent in the pulverized rubber, about which they can do nothing by the time they have obtained it as crumb rubber.
The University of Arkansas did some testing to see if, within a limited value as a sterile mulch, crumb rubber could be categorically declared to be harmless. Drawing paramaters specifically designed to insure positive findings, U.A. indeed "proved" that rubber mulch does not harm plants if used in places where there are no plants to begin with! How could research paramaters become so moronic? In this case, the Horticultural department at the University of Arkansas was specifically hired by Davis Rubber Company so any posturing as an independent study merely compounds the lie.
University of Florida also took funding from Florida rubber mulch manufacturers to "prove" something positive about the product. Whimsically their "best" spin in the products' favor was that it was good for permanent landscape features where a landscaper wanted nothing to grow. Even at that they recommended it be mixed with gravel to limit this lightweight crud's migration into areas where it could cause harm.
It's no accident that Florida, the Carolinas, & Arkansas are the places where this stuff first gained "popularity" or was first marketed successfully, as that is the part of the USA populated by nine-fingered chicken factory workers & where open cesspools of pigshit are seasonally flooded into watersheds by hurricanes & where once-beautiful hills & valleys have been leveled by coal stripmining companies. Universal concessions to anything Industry demands has never benefited citizens of the South, but it has lined the pockets of politicians.
Waste Management Acts in southern states dealing with used tires were the first to encourage novel & creative uses of crumb rubber without regard for the dangers. The southern states even provided the first markets for the dubious products, to whit:
South Carolina's Three Rivers Solid Waste Authority was the first major client for rubber waste dumped over great areas of land at highway rest stops. The S.C. Department of Health & Environmental Control's Office of Solid Waste Reduction & Recycling put their own PR department to work promoting a potentially harmful waste product as the Ultimate Solution to the problem of used tire disposal.
When Rubber Barons can get local government officials to spew their propaganda for them, how much nicer it all works out for the Rubber Barons.
A three year slipshod "study" in South Carolina was an amazing white-wash job. The primary "plus" finding was that county & state laborers & groundkeepers liked the stuff because it lessened the amount of work they had to do, since rubber never leaves the environment the way organic mulches do & doesn't need re-applications. This is a little like giving a clean bill of health to Sterno as a food product because some hobos said it was good to drink.
Although the PR spin was that "no problems were reported," the study actually did note (framing it as an unimportant aside) that rubber mulch killed all the flowers in summer. All of them! The study further noted that the rubber mulch smelled bad on hot days (failing, however, to note that the fumes are toxic). But the primary conclusions made the important factors for the continued use of rubber mulch these: 1) Its permanency in the environment; 2) It keeps its color; & 3) some rest-stop laborers were glad they didn't have to mulch as often.
When studies are arranged to assess how long it lasts without fading, rather than how it harms the environment, really great things can be said about rubber mulch!
South Carolina's waste management agency next went out of its way to promote the product in other states & spread the project to kill the flowers & stink up the rest stops all across the continent. They already had their own state's waste tires ready to ship! Woohoo!
The South Carolina study also admitted that producing this stuff is one of the most expensive uses of public funds. But was that a negative? Certainly not! It was no big deal because the state government could charge every tire buyer a special tax on every tire sold in the state to underwrite recycling. Rubber mulch is good because it raises taxes? Sheesh; & politicians wonder why they're despised.
So the industry coopted to their point of view such diverse folks as child safety people (because rubber mulch under Lollypop Land swing sets made falling down a trampoline act); government waste management people (who'd long ago taken on what should've been the industry's responsibility to get rid of waste tires), recycle environmentalists (who'd buy candybars made out of deep fried dogshit if it said "recycled" on it), as well as sleezier sorts of smaller business opportunists informed that it was legal for them to cheaply obtain a toxic waste product to repackage for sale to gullible gardeners.
When the Arkansas Attorney General recommended rubber mulch for state playgrounds & parks, it was because Davis Rubber was a local employer. When a government department or University study is not bought & paid for by the industry, the condemnation of rubber being strewn into the gardening environment is entirely clear (as it is clear from Ellen Harrison's research at Cornell University Waste Management Institute). The industry generates its own "alternate" studies then promotes only those.
The rubber industry greased the palms of many activist organizations & university departments to focus on finding values & stop condemning the stuff for its negative effects. Richard Evans of the Horticultural Extension of Davis University in California put the best spin he could on his study of potting soils made with crumb rubber. All glowy-eyed in one interview he said how really well the chrysanthemums grew in this potting medium, saying: "It works pretty well. It has some nice properties."
Pressed for details, he less happily admitted, "The only problem was, the zinc content began to kill the chrysanthemums." It took one week for the plants to show evidence of toxification & browning leaves. And that wasn't even with repeat use — just one good dose of crumb rubber & kaput.
How could he interpret a crumb rubber planting medium that kills the plants as in any way "a nice property" for the product? Check out how much funding scattered throughout the University of California system comes just from Goodyear Tire & Rubber. Davis University in particular is looking to hire more lab technicians with, to quote from their own employment opportunity webpage, "Demonstrated experience & knowledge of nylon, acrylic, polypropane, polystyrene, natural rubber, styrene-butadiene rubber, acrylic-butadiene rubber" & so on. These are the growing areas of research that can be fully funded by industrial grant-monies. Slowly it becomes clear how rapid decline of plant health might be found to be "a nice property" for crumb rubber.
Government & university assistance to the rubber industry is even more absurd in some other countries. In Malaysia all government rubber policies are oriented toward benefiting the sizeable rubber industry, which has resulted in a considerable problem of waste tires. For some while this fuel was even used by bakeries, until the public balked at rubber-flavored breads & pastries.
The Malay government had encouraged through funding research on what to do about the growing problem of rubber waste, resulting in the the public being encouraged to buy & use a recycled rubber fuel which fouled the atmosphere. Just as for the American promotion of toxic rubber mulches for the garden, Malaysia too found a use for old tires with the same underlying philosophy that the environment does not count, even the quality of the food we eat does not count. All that matters is solving a waste management problem in a way that profits rather than taxes industry.
Easy inroads have also been made in Argentina, where crumb rubber is presently being touted as a "natural" or "organic" fertilizer. That can be made to sound like a reasonable claim since rubber is presumedly a tree product to start with. This conveniently overlooks the fact that tires have not been manufactured from pure rubber for decades.
Much more recently a reasonable use for rubber tires was developed in the United States: as a fuel to generate electricity, replacing coal, in special electrical plants using special scrubbers to keep the pollutants out of the atmosphere. A few such plants could take care of the rubber waste problem profitably & with minimal harm to the environment. But as it turns out, the price-value of rubber as an electricity-generating fuel is a tiny fraction of its highly inflated price when sold to public to smear on gardens. State of the art electrical generators cannot compete on the open market for waste rubber, not now that sleezy small businesses have gotten so well established. It remains more profitable to hoodwink citizens into poisoning their gardens.
The real answer is to formulate & manufacture tires in such a manner that they are recyclable into making new tires out of old. As presently formulated this is impossible, & neither the oil tycoons nor the rubber barons want this to change because it is vastly more profitable to keep providing new raw materials.
Crumb rubber factories are being opened in almost every state of the union because the government has accepted this as the best answer to a solid waste problem with economic side-benefits. Many a so-called "environmental" project can be turned into an opportunity to spread out more crumb rubber. It's now being used in wetlands "restoration" projects for example. Vast amounts of tire waste are being dumped into wetlands despite studies that show it only takes one week to start killing native plants.
The best we can hope for is that organic gardening will become so widespread that the governmental & industrial desire to dupe us one & all, merely to sell us stuff with which to injure the environment, will in the long run fail. So far, alas, it looks like they're having a rousing success getting gardeners to do their dirty work.
Footnote & References:
The above article was first published on-line in 2000, with periodic up-dates that caused it to get longer & longer. When first posted, a google search would get a seeker hundreds of vendor-generated articles & virtually nothing factual about its deadly Zn toxicity to plants, the disgusting odor that would ruin anyone's pleasure in its vicinity, & the fire hazard rubber mulch constitutes. Today, however, there is increasing information all over the web, & the news is slowly getting out, though the weight of vendor misinformation still exceeds the availability of factual information.
The article still generates more letters of comment than any other single piece at paghat.com. The most common & most tragic letters are from people who found out too late how awful this stuff smells & how it killed their plants, & how difficult & expensive to reverse the error & get this crud out of their landscapes.
Once I got a letter from a vendor threatening me for ruining his business, stating that if I didn't immediately remove the article from the web, he would sue me. I gave him my name & home address & invited him to start legal procedings at once, as I would enjoy owning his house when all was said & done. I never heard from that puling garden-killer again.
Individuals who have had their gardens destroyed by this stuff have been taking landscapers to small claims court, & I'm often asked for further citations so that good scientific data could be presented to the judge. Some of the articles I read for the original article circa 1999 I did not keep copies of, & don't want to go back into the library just to compile a more complete list of citations (I attempted to cite, within the article, enough for anyone with deeper interest to track down my sources in any good science library). But here are a few additional references about the dangers of rubber mulch, for whoever needs them:
Bowman, D.C., R. Y. Evans & L. L. Dodge: "Growth of chrysanthemum with ground automobile tires used as a container soil amendment" in Horticultural Science 29, 1994.
Bush, Edward, K. Leader & A. Owings: "Foliar Accumulation of Zinc in Tree Species Grown in Pine Bark Media Amended with Crumb Rubber" in The Journal of Plant Nutrition 24, 2001.
Chalker-Scott, Linda: "The Myth of Rubberized Landscapes: 'Recycled rubber mulch is an environmentally friendly, non-toxic choice for landscapes'," in Horticultural Myths Sept. 2005, on-line column, Puyallup Research & Extension Center, Washington State University.
Chaney, Rufus L. "Zinc Phytotoxicity" in Zinc in Soils & Plants edited by A. D. Robeson (The Netherlands: Kluwer Academic Publishing, 1993).
Chaney, Rufus L. "Re: Tires," commentary at the Sustainable Agriculture Research & Education bulletin board (link provided above), 1997.
Foy, C. D., R. L. Chaney & M. C. White: "The Physiology of Metal Toxicity in Plants" in Annal. Review of Plant Physiology 29, 1978.
Handreck, A.: "Zinc toxicity from tire rubber in soilless potting media" in Community Soil Science Plant Anals 27, 1996.
Hodel, Lindsey: "Gardeners, Tread Lightly" in Mother Earth News Green Gazette, April/May 2003.
Schulz M. "Effects of ground rubber on Phaseolus vulgaris" in Z Pflanzrnahr Bodenk 150, 1987.
Stewart, Larry: "Is Your Landscape Going up in Smoke?" in Ornamental Plants Annual Reports & Research Reviews, 2002.
Tucker, M. Ray: "Ground Rubbed: Potential Toxicity to Plants" in North Carolina Agriculture & Consumer Services Agronomic Division Nursery Notes April 1997.