Is rubber mulch safe for flowers, plants and pets

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This article explains the benefits and risks or dangers of using rubber mulch in landscapes and gardens.
by Maple Tree · All Zones · Product Reviews · 5 Comments · March 28, 2013 · 9,209 views

Is rubber mulch safe for flowers, plants and pets

Research at Bucknell University has found that the leachate from ground tires can kill entire aquatic communities of algae, zooplankton, snails and fish. Even at low concentrations it can cause reproductive problems and precancerous lesions. Also, marine life from seaweeds to plankton is negatively affected. The toxic nature of the leachate from tire rubber is due at least in part to the chemicals used in producing tires (cadmium, chromium, aluminum, copper, iron, manganese, molybdenum, selenium, sulfur, and zinc). Of these minerals, rubber tires may contain extremely high levels of zinc even up to 2% of the tire mass. Many plant species have been shown to accumulate zinc in their tissues to the point of death. USDA researchers who have studied the effects of metals in sewage sludge, biosolids and compost, have found that ground rubber should not be used on any agricultural or garden soil, potting media, or compost. Yes- some companies use tire chips and crumb rubber as a bulking agent for compost and we wonder why the compost does not work and is toxic to plants! Other rubber leachates have been found to cause problems from skin and eye irritation to major organ damage and even death. Long term exposure can lead to carcinogenesis and mutagenesis. For example, 2-mercaptobenzothiazole used in vulcanizing rubber is highly persistent in the environment and harmful to aquatic life. Ground rubber also contains a class of chemicals called Polyaromatic hydrocarbons (PAHs) that many studies have found extremely toxic to humans and the environment. Research has also found that the toxicity of leachate from the rubber tire mulch increases over time as the rubber breaks down.

Water and nutrients permeate

Some researchers have found that ground up tires can absorb chemicals from fertilizers and pesticides preventing them from leaching into ground water. Hence, fewer nutrients reach the plants. Eventually, the tire chips will degrade and the stored chemicals will be released most likely at time when one does not want or need them. Water will run through the tire mulch as it is highly permeable. However, the problem begins when the water reaches the surface of the soil. Earthworms and soil microbes create soil structure allowing air and water to enter the soil. Earthworms and microbes require decomposing organic matter as a food and energy source. Without this food source most of the earthworms and microbes will die off and the soil structure will collapse over time. When this happens, the soils will become anaerobic (favors root pathogens) and water and air cannot enter easily. Hence, conditions may be created that favor disease and since the water can no longer be absorbed, it must run off.

Improves landscaping

I am not sure what is meant by this claim. Consumer Reports Magazine found that some of the rubber mulches tested faded during the tests. Personally, I do not like the bleached out look. The USDA Agricultural Research Service, after over 20 years of research concludes that on the zinc factor alone, ground or chipped tire material should never be used in gardens or landscaping. How can a material that kills many types of plants be classified as “Improves Landscaping” unless one likes a barren and sterile yard.

Many designer colors available

This is a true statement. Rubber can be painted to almost any color. On whole tires paints tend to peel or rub off over time. I wonder what is in the paints or dyes used on tire chips and how long they will last. One study found that tire chips started fading fairly quickly.

Saves time, money and your back

Let’s look at saving money. Consumer Reports found that prices ranged from $13.75- $15.00 per cubic foot for various brands of rubber mulch (the average wood mulch was only $1.50 per cubic foot). This works out to over $400 per cubic yard! A person can buy a extremely high quality composted and screened “Native Mulch” or “Compost” for less than $35 per cubic yard in bulk. Native mulch or compost improves soil quality reducing a plant’s water requirement by 50% or more which saves money. They also provide nutrients and help a plant become healthier (less disease and insect problems) again saving money. The plants grow much faster so a smaller plant (lower cost) may be purchased again saving money.

I wonder what happens as leaves and grass are blown onto the rubber mulch. In organic mulches, one would just rake it up and if a few pieces of wood chips get mixed in, who cares as it all goes into the compost bin. But with rubber mulch how does one get the tire chips out and at $400/cy it is very expensive to waste. Since chipped tires are heavier than water and organic mulches, it means it takes more work to move and spread them. Coupled with the extra cleaning required to keep them looking nice, I wonder how this saves your back. Also since it is not available in bulk, one must load it into your car, unload it when you get home, and then tear open the bags and spread it (less work?).

A few other studies have looked at soil temperature under rubber mulch as compared to other types of mulch or bare ground. If the rubber mulch is several inches thick, then soil temperatures are not excessive, however, the instructions on some bags say to apply only one inch thick. If used at the required thickness (3”) to keep the soil cool, then the cost would triple and there would be far more toxic material on your property.

Good for playgrounds (twice the cushioning effect of sand or gravel)

Consumer Reports found that the rubber pieces contained small pieces of steel and nylon and recommended it not be used for playgrounds. One study comparing rubber mulch to organic materials like wood chips, used double ground bark and uniform wood chips as their reference. For a mulch to be effective for playgrounds, it needs to be loose without any fines to prevent compaction and keep it springy for shock absorption. Double grinding a bark mulch creates a lot of “fines” that will help the mulch pack hard and tight as it fills in all the open areas. Barks also tend to be hard and brittle, not flexible like ground branches and limbs which are often used for playground mulch and do not contain any toxic chemicals. Similarly, uniform wood chips from a chipper, since they are thin and flat (versus long and stringy from a grinder), would also pack down hard and tight (of course uniform wood chips are not a good choice for playground mulches). Other comparisons included sand and gravel which are illegal in many states for use as playground mulch. Since rubber mulch does not mat down or lock together, it will easily escape the playground area and migrate into the surrounding lawns or flowerbeds. I remember when I was a boy, I used to enjoy throwing the rocks used in playgrounds and they usually did not land in the playground area. I wonder how the chipped tires would look scattered across a lawn or driveway next to a playground.


Jocko Johnson

Jocko Johnson · Gardenality Seed · Zone 8A · 10° to 15° F
That article is from 2005, if not older. Since you pretty much copied and pasted from it, did you look to see if there were any advancements in rubber mulch? I am not for or against its use. I was doing online searches for pros and cons of rubber mulch. I did a broad search (no date ranges) and noticed the natureswayresources.com article. Then I set the date range to within the past year. Your article came up and it said the same thing. Thanks for being useless.

6 years ago ·
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Maple Tree

Maple Tree · Gardenality Genius · Zone 10A · 30° to 35° F
Jocko-As stated this article was based on Mr. John Ferguson's (Nature's Way Resources) article. Because of this it should be posted somewhat as is. After speaking to a horticulturalist on their staff and receiving Mr. Ferguson's authorization to post his article it was evident to me the research is still credible with them. I couldn't find any other that has changed my own mind regarding the rubber mulches. Quality nurseries in my area do not carry the rubber mulch products and because of this I felt more research on my part should be done before using it myself. There are other articles in Gardenality that explain the benefits of these products that I hope all will read also. This article was posted, as was said, in hopes of stirring concern and research on individuals part to determine what products they feel is best for their landscapes and gardens. Thank you for reading the article and researching these rubber products on your own. The article has evidently been successful in bringing forth your concerns and because of this I don't feel it was useless. Hopefully your research will help in adding to the pros and cons of these products. Possibly an article that will help all of us determine this products useful place as recycling is a concern of all of us.

6 years ago ·
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Jocko Johnson

Jocko Johnson · Gardenality Seed · Zone 8A · 10° to 15° F
Thanks for taking the time to respond. Perhaps I was too harsh at first to say it was useless. However, I have looked up a few different pieces of info that I could find probably biased sources - but found that advancements were made to at least the toxicity or lack thereof in some brands. I still am trying to determine what is best. I am leaning towards recycled still but want to make sure it is the right decision for me.

6 years ago ·
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Maple Tree

Maple Tree · Gardenality Genius · Zone 10A · 30° to 35° F
Unfortunately there still has been very little research regarding the effects of rubberized mulch on plant life. Most research has been done on rubberized mulch used in athletic and recreational applications, including ground cover under playground equipment, running track material and as a soil additive on sports and playing fields. Besides the rubberized mulch used in our gardening and its effect on our plantlife its useage in the human invironment is also very important. Below are a few other resources found that some may be interested in reading.

http://center4research.org/child-teen-health/early-childhood-development/caution-children-at-play-on-potentially-toxic-surfaces/

http://en.wikipedia.org/wiki/Rubber_mulch

http://www.finegardening.com/its-red-its-rubber-it-safe-your-garden

http://online.wsj.com/articles/SB121362884056577645

4 years ago ·
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