Wood Mulch vs. Rubber Mulch: What the Research Says
Rubber mulch is marketed primarily on longevity -- it will not decompose, will not float away in heavy rain, and holds its color for years. These claims are accurate as far as they go. But longevity is not the only criterion that matters when you are putting material in direct contact with plants,.
Rubber mulch is marketed primarily on longevity — it will not decompose, will not float away in heavy rain, and holds its color for years. These claims are accurate as far as they go. But longevity is not the only criterion that matters when you are putting material in direct contact with plants, soil, and the root zone.
Wood mulch decomposes and that decomposition is not a flaw — it is a feature. What replaces wood mulch as it breaks down is organic matter, and organic matter is the foundation of soil biology. Rubber adds nothing to soil and, under certain conditions, leaches compounds you do not want near food crops.
What Each Product Is Made From
Wood Mulch
Wood mulch includes a range of products: shredded hardwood, wood chips (from tree trimming operations), bark nuggets, cedar, pine straw bale, and cocoa hull mulch. Per Penn State Extension, each type differs in decomposition rate, pH effect on soil, and suitability for different plants.
Shredded hardwood and wood chips are the most widely recommended for general garden use because they decompose at a rate that builds organic matter without tying up nitrogen excessively.
The feed-and-forget option
Osmocote coated prills feed for 6 months on a single application. Balanced N-P-K, won't burn roots. Read our full pick.
Rubber Mulch
Rubber mulch is shredded recycled tires. Per Penn State Extension, a standard car tire contains approximately 25% carbon black (a possible carcinogen), steel wire (removed before shredding in most products), zinc in concentrations of 1–2% by weight, and a range of organic chemical compounds including benzothiazole, butylated hydroxyanisole (BHA), and various aromatic hydrocarbons.