Rubber Mulch: Where the Rubber Meets the – Soil?


At Costco recently, I was happy to see some acquaintances coming out of the garden section, until… what in the WORLD was in their cart? It looked like bags of mulch, but… wrong somehow.

They patiently explained to this landscaper that recycled rubber mulch is the newest thing and would look very pretty in their garden beds.

I was speechless. Over the years I’ve prepared a number of gardening speeches to help my hapless friends make better gardening decisions – “Why that cute little redwood won’t do under the eaves”, for example, and “Please stick the ivy in a pot”.

“Why putting ground-up old tires on your garden bed is a bad idea” is one I never expected to have to deliver. I mean, recycling old tires is a great idea, but… they don’t break down, do they? And what about all the chemicals?

After sputtering some shocked words (“Think of the earthworms!”), I went home resolved to research the issue more thoroughly and find out if the stuff is really as bad as it seems. Heck, maybe there’s some cool new processing trick that removes the chemicals and turns the rubber into fertilizer-holding goodness for your soil. Perhaps I was jumping to conclusions?

I was relieved to find that Linda Chalker-Scott, author of The Informed Gardener and one of the leaders in bringing a scientific approach to the often superstitious practice of gardening, had just written a piece on this subject.

I found that rubber mulches are indeed made with dyed, ground-up old tires. They aren’t processed or treated in any special way to remove the harmful chemicals – they’re just, well, tires.

But what’s wrong with using them as mulch, you may ask? Linda says:

  • It’s not effective: Studies have shown that organic mulches such as wood chips and straw are more effective at holding down weeds than rubber mulches.
  • It’s toxic: Not only is it toxic to aquatic life when the runoff leaches into water, but the high concentrations of heavy metals such as zinc in tires can harm or kill your garden plants. Not convinced? Chemicals found in tires are also hazardous to human and animal health, so your rubber-mulched garden beds might not be the safest spots for your kids to play.
  • It’s a fire hazard: Tires have some very flammable compounds in them, and prove difficult to extinguish once ignited. Turns out rubber mulches retain that same quality and are more difficult to extinguish than any other mulch.
  • It stinks: When the sun heats rubber mulch, it stinks. (And I don’t even want to hear it about compost stinking. That’s not the same and you know it!)

I’ll add that part of the point of using a mulch is that it slowly breaks down and enriches the soil, encouraging earthworms and other good things to flourish. Rubber mulch does none of those things.

Go on over and read Linda’s article, and if you like, you can check out the more scientifically-worded paper she wrote for the Washington State Research and Extension Center.

photo credit: on Flickr



  1. says

    I’d wondered about those rubber mulches. I wouldn’t have used them myself, partly because I believe in building soil with organic material, partly because I’m well aware of how tires stink in the heat. Thanks for writing this up; it’s really good for us to think through what we use and it helps a lot to have information like this available.
    .-= Pomona Belvedere´s last blog ..Strawberry Jars: Killer Pots? =-.

  2. Susan Fox says

    Rubber mulch. Yuk. Doesn’t break down and how would you ever remove it if it became a problem? Something else that superficially sounds good- a way to recycle gazillions of old tires- but isn’t, once you look at the consequences.

  3. says

    Pomona, yes, I am such a fan of organic material that I hardly knew what to say to my friends when they bought the darn stuff. It not breaking down seemed to be a benefit in their minds, but – all I could think was about the dead sad soil they’d leave.

    And Susan, you are so so right about the removal if it became a problem or if tastes change. Seems like most landscapes that need to hire a pro for demo-ing have some non-breaking-down thing that became a problem – red lava rock, for example. It costs money to apply and then money to remove, without providing much benefit along the way.

    And removed rubber mulch would go straight to the dump – can’t even use it for fill I don’t think. People often forget to think about these things, but it won’t stay pristine and effective forever, so the end of the mulch’s life is important to consider.

    Linda – thanks so much for commenting and for writing those excellent articles!! Such an important topic, and I love your new blog.

  4. says

    I don’t think it should even be called mulch. Like you said, a big part of mulch is that it breaks down and feeds the soil. Anything that doesn’t fill that purpose should not be called mulch. I didn’t know it was a fire hazard. That’ll be a good one to discourage people.

  5. says

    yuck, yuck and yuck. I can’t imagine any gardener putting that down in their garden! It’s just a huge oxymoron!! I would imagine it would smell a little ‘rubbery’ on a hot day? And why wouldn’t someone want to amend their soil with natural substances? I just don’t get people…

    Thanks for writing such an informative piece – I’ll bookmark this for sure, as I’m sure I’ll get asked about this at one point or another…
    .-= rebecca sweet´s last blog ..What I keep in the trunk of my car… =-.

  6. says

    We’ve had quite a few request for this in our nursery – now I have even a better come back on why not to use it. My main concern was getting it out of the soil ’cause you know its going to work its way down and the cost always seemed excessive for “mulch”. Thanks for researching!!

  7. says

    I am so glad this provides you with a comeback, Kris! If you want to print it out and give to folks at the nursery, the Print This Post link at the bottom gives a printer-ready version complete with writing out the links for further research!

  8. says

    Thanks for this mulch tip. I was searching the website for “fire safe” mulch and this article came up in the search. I am trying to find a mulch that I can use that is considered “fire-safe” since I live on the edge of a “forested” area. I love the wood mulches but these burn so I can’t use them. I’ve thought of the “rocks/gravel” alternative but would rather not go that route if I can find a more soil friendly alternative. Any suggestions?

    • says

      I sure wish I knew, Patricia. But I live in a very rainy part of California so have never encountered the need for fire-safe mulch. I did a bit of looking around on two sites that I trust – Dr Linda Chalker-Scott’s site and and haven’t found anything useful. I wish you the best in finding this info out – you know what I’d do? I’d call your local agricultural extension office in the phone book and see what they have to say. I bet they have a large amount of info that is regionally appropriate.

  9. Shelley says

    I appreciate the info you’ve provided about Rubber Mulch. I don’t have a garden, but was considering it around the front of the house and around trees. My biggest concern was if it would stink like, well, TIRES…. Guess my question was answered. Thank You, Thank You. Real Mulch it is.

  10. says

    I just spotted this article on rubber mulch, and am glad someone is taking a stand! What we have here is manufacturers finding a way of helping folks to indulge in their natural tendency to avoid work. Now, I’m all for making things easier: by mulching, using native plants and techniques, etc. But rubber in the garden? That just doesn’t make sense, and it shouldn’t take a rocket scientist (or a gardening expert) to figure that out.

  11. Ed says

    I have rubber mulch and love it. Now if i was a professional gardner or avid home gardner maybe I would enjoy the yearly mulching and the ever thicker layer of “decomposed” mulch in which more weeds grow. But for me it looks great, doesn’t decompose and that is the big plus. Rubber mulch only ignites with an open flame – not with a cigarette dropped in it. How many mulch fires have you ever heard about in the 1st place? If you use a weed block fabric before you mulch (like you should) the rubber mulch will not mix into the soil and could be removed if desired. The rubber smell, just like any new mulch smell when just laid down, is gone in a few days – does your garage smell like rubber? As to dangerous chemicals – well from research to date rubber mulch contains less than what is already present in the soil. So if you are an avid gardner then feel free to hate rubber mulch – for the rest out there it saves a lot of yearly work and looks great.

  12. says

    I agree with above. Rubber mulch is amazing. Everyone is worried about pollution? Who cares. Why just push pollution away to a junkyard. Put some in your garden and at least enjoy its visual beauty. Tires smell great. Awesome way to make husbands like me happy. And as for healthy soil. A few bags of peer, sheep shit and miracle grow will out do your ugly mulch any day. Rubber is a winner.

  13. Dave Turgeon says

    Last year, I constructed a patio and connected paths using rubber mulch over a cloth weed barrier. This, I think, is the best use for rubber much. It is less expensive than hard surface alternatives, is easy to install and maintain, is durable and weathers well, is comfortable under foot, and has no water pooling or weed problems. My garden beds are mulched with brown wood chips, to complement the brown rubber mulch. A brown, 4″ high, flexible rubber edging/barrier (also made from recycled tires) separates the rubber mulch from the wood mulch. I had originally planned on using gravel for the patio and paths, but the rubber mulch worked out so much better.

  14. Stacey says

    I remember they used rubber mulch on the play ground in gradeschool under the slides and swings and things. It was a horrible idea. It stank and all the kids would come home with their shoes full of it. Now I’m learning it was probably toxic, as well! I guess the idea was that if someone fell down, they wouldnt get hurt, or maybe they were supposed to bounce.

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