The zinc in rubber tires leaches into the soil and is probably toxic to plants and humans. ===== It sounds like an environmentally friendly way to liven up your yard or garden: rubber mulch that's made from recycled tires. Rubber mulch can be use mostly the same way as any other mulch whether it's for landscaping, gardening, or children's playground. Most companies that manufactures rubber mulch labels it as a safe, economical and long-lasting alternative to regular wood mulch. Even my neighbor was trying to get me to buy into the whole rubber mulch idea as I spoke to him the last week. But is it really environmentally friendly as many companies claim it to be. According to a study by Linda Chalker-Scott, Ph.D. an Extension Horticulturist and Associate Professor at Washington State University states that. "Rubber mulches are touted by manufacturers and distributors as permanent ("doesn't decay away") and aesthetically pleasing ("no odor" - "looks like shredded wood mulch" - "earth tones and designer colors" - "special fade resistant coating") landscape materials. Furthermore, we are told that rubber mulch is "safe for flowers, plants and pets" (though it "doesn't feed or house insects") and "dramatically improves landscaping." It seems to be an environmentally-friendly solution to a major waste disposal problem." That's the myth of rubber mulch if you choose to believe the myth of the matter; it isn't as safe as you might think. Linda Chalker-Scott, Ph. D. further states, "Rubber mulches have not proved to be particularly good choices for either horticultural production or landscape uses. In comparison studies of several mulch types, rubber tire mulch was less effective in controlling weeds in herbaceous perennial plots than wood chips. Similarly, sawdust made better mulch for Christmas tree production in terms of weed control, microbial biomass, and soil chemistry. Another comparative study found rubber to be less effective than straw or fiber mulch in establishing turf grasses." If you think rubber mulch is still safe to use compare to the other organic mulches, grounded rubber is more likely to ignite and more difficult to extinguish. So in areas where natural or man-made fires are likely to happen rubber mulch should not be used. Mulching Options Rubber: Pros: Uses recycled tires and saves trees, can be dyed to match landscaping, long lasting. Cons: Cost higher than wood mulch; adds little nutritional value to plants and can add harmful zinc to plants. Wood: Pros: Depending on blend, can add a lot higher nutritional value than rubber or rock mulch; good value for the money. Cons: Has to be laid at least once a year due to decomposition. Rock: Pros: Best used for desert type plants. Cons: Offers no nutritional value; Must prepare to install rocks by first using a layer of weed mat that will act as a mulch agent. According to one USDA researcher who has studied zinc and other metals in soils and plant materials for decades strongly believes that ground rubber should not be used "in any composting, or in any potting medium, or casually dispersed on agricultural or garden soils" because of zinc toxicity. Studies have shown that rubber leachates are a very complex and can be damaging to humans either in short-term or long-term exposure in high enough concentrations. Linda Chalker-Scott, Ph.D. basically had this to say about rubber mulch. Rubbermulch is not as effective as other organic mulch choices in controlling weeds Rubbermulch is highly flammable and difficult to extinguish once it is burning Rubbermulch is not permanent; like other organic substances, it decomposes Rubbermulch is not non-toxic; it contains a number of metal and organic contaminants with known environmental and/or human effects. The Myth of Rubberized Landscapes Linda Chalker-Scott, Ph.D Here is a link that might be useful: Busting the Myth of Rubber Mulch as a Safe Alternative

I'm starting to get a little P.O.'d that my replies keep getting toasted...had a nice long reply to this thread several days ago and I come back and notice it's not here. This'll be like the fourth or fifth time that's happened to me in the last two weeks. ----------- I like and recommend peat moss. Mushroom compost is too expensive and doesn't serve any "additional" benefit that the grass will be able to leverage. All of your experiences with straw are the same reasons why I've hated to use it. Although, if you go through the trouble to cut your straw up into 3-4" segments, it'll work just fine but I don't know anyone that would go to that level of trouble - not when peat moss is so cheap. The nice thing about peat moss is that while it's incredibly hydrophobic the first time you water it after you get past that first, initial watering in it will retain moisture like no other mulch can. It will also tell you in plain, easy to see signs when and where it needs more water. Wet peat moss looks like wet coffee grounds and dry peat moss looks like dry cocoa powder. How easy is that?!?! Also, contrary to popular believe, once you've gotten it thoroughly watered in that first time it will not blow away in the wind if it gets dry. It'll stay in it kind of "mat" that only a good torrential downpour could wash away, but then again anything else you laid down would wash away too so it's not an inherent fault of peat-moss really. ---- Two other things... The device you were looking for is sometimes called a "compost roller" / "topdressing spreader" and they're only carried online and cost about $100-120 each plus shipping. I need to spring for one myself soon for future top dressing applications but damn what a PITA it'd be to store it. Some googling will produce images/retailers. Also, when dchall recommends a water-filled roller, I'm sure he meant to include that there should only be a couple gallons of water. Just enough that it's light enough for a man to lift it but not much lighter than that. Typically this is about 1/3rd full but obviously that depends on the capacity of your roller's drum. --- Cannot stress how hydrophobic peat moss is that first time. I've heard/read a lot of stories where people didn't water in their seed enough because they didn't realize that their 1/4" thick layer of peat moss could take over an hour of watering and still not be soaked all the way through... Here's what my peat moss mulch based KBG renovation looked like after three weeks. I just think it's so much cleaner than straw... :shrug:

Not too many years ago tire dumps were considered Haxardous Waste Sites and after the tires were removed the soil was also because that soil had higher than permissible levels of Cadmium, Lead, and other heavy metals. So someone develops a way to finely shred tires and sell it as a mulch and suddenly putting tires on your soil is not a problem, however, playgrounds that did put shredded tires down fairly quickly removed that material when it was found to children were being exposed to higher than normal levels of Cadmium, Lead, etc. and that the urine of soccer and football players playing on artificial turf (made with, or from, recycled tires) had higher than normal levels of carcinogens. Aside from the simple fact that this shredded rubber will not add anything of value to your soil, there may once again come a day when this material is recognized as the Hazardous Material it still is and require removal, at your expense.

Zinc could have various forms in this situation - metallic, or as a salt for example. Or corroded zinc metal (zinc oxide). (There are even organo-zinc compounds but I don't know if these occur in tires). These will all behave differently in the same type of soil. Superimpose differences in soils and it gets even more complicated. Assessing the risk from soil alone (direct exposure by passive ingestion, inhalation of dust, and dermal contact) is usually based on total concentrations (regardless of form), perhaps an oversimplification but at least it gives some results to work from. Gardening (i.e. eating plants) is more complicated. Different plants will uptake the various forms of metals at different rates. Any chemical, once taken up into the plant, may or may not degrade (obviously with zinc this isn't a question) and will also be deposited in different parts of the plant at different concentrations. To do a human health risk assessment, you'd have to take all this into account to estimate a dose from eating even a single type of plant out of a garden. Multiply all that by the hundreds of chemicals typically addressed at polluted sites, times all the vegetables you might grow, and it becomes an enormous task. About the only one we know very much about is Pb since it's been studied to death. You can actually correlate blood lead levels to soil concentrations as well as toxic effects, and as a result it's the only contaminant to have safe levels in soil directly based on known health effects. For everything else, there's a crap ton of modeling in between.