Rubber Mulch
Rubber mulch is a landscape mulch material produced from recycled rubber, most often ground from scrap tires. Institutional guidance on using it in landscapes is not uniform: Washington State University Extension advises against using rubber as a landscape amendment or mulch, while Mississippi State University Extension and Clemson Cooperative Extension list it among landscape mulch options with noted advantages and disadvantages. Extension institutions also describe its persistence differently: Clemson and Mississippi State describe ground rubber tire mulch as long lasting and not biodegradable, while Washington State University and University of Illinois Extension describe it as not permanent and subject to microbial breakdown. Washington State University and University of Illinois Extension also report specific, documented concerns under particular conditions — including zinc and other metals identified in laboratory and field leachates, and effects observed in some plants and soils — without amounting to a universal safety verdict. Working out how much rubber mulch to buy and how deep to spread it are handled by dedicated pages elsewhere on this site, and playground safety and comparing rubber mulch against other mulch materials are outside what this page covers.
What Rubber Mulch Is
Rubber mulch is a landscape mulch material produced from recycled rubber, or scrap-tire material, at the scope Extension sources describe. Institutional sources refer to it using terms such as ground rubber, ground rubber tires, and recycled rubber tires. What any particular bagged or bulk product labelled rubber mulch actually contains — including whether it is entirely tire rubber, free of wire or other metal, or produced to one standardized composition — is not something this page states; no Extension source describes a universal composition standard for commercial rubber mulch products.
Rubber is also used for playground surfacing, covered on a separate page.
How Extension Sources Describe Its Persistence
Extension institutions describe how long rubber mulch lasts differently. Clemson Cooperative Extension states that mulches made of ground rubber tires do not decompose and, unless the material scatters, may never need to be replaced. Mississippi State University Extension similarly lists recycled rubber tires as long lasting and not biodegradable. Washington State University Extension, by contrast, reports that rubber is broken down by microbes and states that assuming rubber mulch is permanent is a fallacy. University of Illinois Extension likewise describes rubber mulch as not permanent, noting that breakdown products — including heavy metals, plasticizers, and accelerators — are released as it decomposes. Clemson itself notes that its effectiveness as a mulch and its color retention are still being evaluated, so this page presents both institutional positions rather than treating either as settled.
Landscape Use: Guidance Is Not Uniform
Guidance on using rubber mulch in landscapes is not uniform across Extension institutions. Washington State University Extension concludes that rubber should not be used as a landscape amendment or mulch. Mississippi State University Extension takes a different view, listing recycled rubber tires among landscape mulch options along with their noted advantages and disadvantages. Clemson Cooperative Extension also lists ground rubber tires among inorganic mulch materials, while noting that the evidence on its performance is still being evaluated. This page reports what these institutions say without adjudicating between them; it does not itself recommend using or avoiding rubber mulch for landscape purposes.
Plant and Soil Concerns Reported by Extension Sources
Washington State University Extension reports that aluminum, cadmium, chromium, copper, iron, magnesium, manganese, molybdenum, selenium, sulfur, and zinc have been identified in laboratory and field leachates from rubber, and that rubber contains very high levels of zinc. University of Illinois Extension reports studies identifying leaf yellowing, reduced tree growth, and increased tree mortality, along with soil tests showing high levels of zinc that can be toxic to plants and could cause leaf chlorosis. Washington State University Extension similarly reports that a number of plant species have been shown to accumulate abnormally high levels of zinc, sometimes to the point of death, with acidic soils particularly sensitive. These are documented concerns tied to specific, studied conditions: Extension sources treat rubber mulch safety as a set of attributed concerns like these rather than as a single verdict for or against the material as a whole.
Other Documented Limitations
Mississippi State University Extension lists heat build-up among the disadvantages of recycled rubber tires used as a landscape mulch, noting that it can retain heat. Separately, Washington State University Extension reports that compared to a dozen other mulch types, ground rubber is more likely to ignite and more difficult to extinguish, and University of Illinois Extension reports that once ignited, rubber mulch is the most difficult mulch to extinguish.
What This Page Does Not Cover
This page describes rubber mulch as a material and deliberately stops there. It does not work out how much rubber mulch you need for a bed or a project — that is the rubber mulch calculator's job. It does not provide a general coverage or depth reference, which the mulch coverage chart covers. And it does not address playground safety or compare rubber mulch against other mulch materials, both of which are outside what this page covers.
Sources
The material descriptions on this page are based on the following sources.
External source links open in a new tab.
- Washington State University Extension — The Myth of Rubberized Landscapes (Linda Chalker-Scott)
- University of Illinois Extension — Contaminated Landscape Materials: Rubber Mulch (Enroth, 2019-09-23)
- Mississippi State University Extension — Mulches for the Landscape (Publication P2301)
- Clemson Cooperative Extension HGIC — Mulch (Factsheet HGIC 1604, rev. 2016-06-20)