QBARS - v35n3 Ground Rubber as Soil Conditioner

Ground rubber as soil conditioner
Fred R. Davis, Kent, Ohio
Reprint from Rubber World

Ground rubber serves the purpose of a soil conditioner or an amender better than it does a mulch. There are also some nutritional benefits from the leaching and bacterial actions.
Several years ago, I did a study using ground tread rubber in growing beds of three-year-old rhododendron. The rhododendron grown in the soil having the incorporated ground rubber produced vigorous foliage and heavy stem growth. There was increased bud set and almost no root disease. Furthermore, the soil remained loose and well-drained with little or no weed growth.
The increased bud set could be explained in terms of the zinc compounds in the rubber. Zinc serves as a micronutrient for the sugar metabolism which is related to bud formation. (See my article in American Horticulturist, Vol. 52, No. 4, Winter '73, pp. 32-35.)
The decreased incidence of root disease is probably related to the fungicidal activity of the residual vulcanization compounds. Commercial materials of the sulfenemide and thiuram type are sold for root rot (Phytophthora cinnamomi), a disease prevalent in azaleas and rhododendron. The better drainage of the soil beds could be explained in terms of the hydrophobic character of rubber, thus the prevention of water logging of the soil.
One must be cautious in using ground rubber as a mulch for azaleas and rhododendron since it absorbs heat and burns the shallow-rooted feeler root system. The heat also solidifies the resins in roots, thus preventing water and nutrient translocation.