Is Rubber Mulch Benificial To Landscapes And Gardens?

A few years ago I noticed a few neighbors of mine were starting to use rubberized bark or mulches in their landscapes and gardens. As an avid gardener I took some time to research as much material as I could find regarding the pros and cons of this rubberized product. The rewards I receive from gardening are enormous and because of this I am always concerned as to the quality of products and their value in keeping my gardens healthy.

Lately I have notice more promotions and articles on the usefullness of rubber mulches. The value of their use in parks, playgrounds, athletic fields, and as infills for synthetic grass sounds good. Working in the automotive industry I am aware of the problems with properly disposing of rubber tires and the huge problems they promote cluttering the landfills. Something definitely needed to be done to find a way to use this discarded rubber. Is this rubber mulch beneficial to my garden or is it a product that may harm my garden plants so they too end up at the landfill or a compost pile?

During my research I found articles published by horticulturists and university extension research centers that were quite disturbing. Researching the use of rubberized mulches I found a most interesting informative article titled "Rubber Mulch-Beware". This article was written by John Ferguson owner of Nature's Way Resources an organically based service company. This article also listed resources that were credible and informative. A few weeks ago while visiting several nurseries and garden centers I noticed the nurseries and garden centers known for their quality products did not carry the rubberized mulches where as the big box stores carried it in several sizes and colors. Could this be telling me something about this product I should know? Hopefully after reading this article you will do some research on your own regarding the pros and cons of rubber mulch. Working in our gardens can produce many rewards. These rewards are a result of hard work, but enjoyable for most, and use of the best quatlity products for healthy plant growth available. Hopefully reading this article, and others you may read, will help you to make the right decision as to whether the rubberized products are ones you want to use in your landscape and gardens.

RUBBER MULCH -Beware

Rubber mulch is typically made from ground up recycled tires and has generated a lot of discussion on the benefits and risks or dangers of using it. There seems to be two schools of thought on rubber mulch. It seems that all the studies paid for by the rubber mulch manufacturers and tire companies show benefits after their PR firms get through with them, while all the independent studies show that it is toxic and dangerous.

So what do we really know about rubber tire mulch?

Here are advertised or alleged benefits of rubber mulch:

• doesn’t float away
• doesn’t blow away
• doesn’t decay away
• doesn’t sink into the ground
• doesn’t feed house insects
• doesn’t smell, mat or mold
• impedes weed growth
• water and nutrients permeate
• safe for flowers, plants and pets
• improves landscaping
• many designer colors available
• saves time, money and your back
• lasts many years
• good for playgrounds (twice the cushioning effect of sand or gravel)
• doesn’t burn plants or children
• cost effective
• safe for children

Let’s look at each of these claims and see what the research says:

Doesn’t float away, Doesn’t blow away, Doesn’t sink into the ground

Most rubber mulches have a specific gravity greater than water hence they do not float or wash off as easily as some other materials like bark mulches. If the soil is healthy and full of microbes and earthworms ALL materials will settle and sink over time (remember Charles Darwin’s work on earthworms). If a material is heavier (denser) than water, it will sink or settle faster than a lighter material like an organic mulch. Research at Texas A&M University found that the particles from shredded brush (i.e. native mulch) would physically lock together preventing erosion even in extreme weather events. Researchers have also found that during decomposition that bacteria produce chemicals called polysaccharides that act as glue to help hold the particles together. The hyphae from many fungus species also help to lock the particles together and to the soil surface. As a result, the native mulch and compost resisted erosion (floating or blowing off) better than any other material tested.

Doesn’t decay away, Lasts many years

Rubber mulch is broken down by microbes like any other product (remember microbes can break down granite rocks into soil), rubber is easy by comparison. The rubber encourages species of bacteria that break down rubber and rubber like products in your home to multiply. The additives in tires to prevent bacteria decay (which are toxic chemicals) are broken down by white and brown rot fungal species that live in soil. This same decomposition is what releases the toxic chemicals in tires.

Doesn’t feed house insects

This is a true statement, I do not know of anything that eats tires except microbes. However, the tire mulch does kill many species of good microbes that kill insects and prevent disease. The toxic chemicals in the tires will also kill beneficial insects that help control pests.

Doesn’t smell, mat or mold

This may be a matter of opinion, but most people find that rubber mulch starts to stink as itgets hotter. On a hot day it has a strong stench. As tires are ground up into chips the amount of surface area is greatly increased and all the new surfaces are freshly exposed allowing for maximum odors to be released. Many people get sick from just being in the sales area of a store selling new tires. As rubber mulch heats up, it releases toxic gases such as volatile organic compounds (VOCs) and another class of chemicals called polyaromatic hydrocarbons (PAHs). These gases have been found to cause irritation of the nasal and respiratory passages, central nervous system damage, depression, headaches, nausea, dizziness, eye and kidney damage, and dermatitis. Hence, ground tires should never be used in an enclosed area or indoors. These effects would be even worse in areas of high air pollution (i.e. Houston). It is true that rubber mulch will not mat down as easily as organic mulches, since the beneficial microbes that create soil structure, prevent insect and disease problems, cannot live in it.
As to mold, I have seen many tires used on piers and boat docks covered with algae. I have also seen tires used as planters covered with what appears to be mildew and mold. Mildew and mold will grow on about any surface if moisture is present, unless it is too toxic and something kills them.

Impedes weed growth

In comparison studies of several mulch types in herbaceous perennials, rubber tire mulch was less effective than even raw wood chips. Other studies have found that even sawdust worked better and have found rubber mulch less effective than straw and other fibers. Several studies have found that rubber tire mulches kill many species of plants hence the public relation specialist spin it off as “retards or impedes weed growth”. Who wanted flowers in the first place? Also as temperatures rises the type of plants that will survive is reduced and rubber mulch can get fairly hot. Metal toxicity also reduces the type of plants that can live and grow in rubber mulch.