Our objective was to determine the feasibility of using waste tire rubber and fiber from the processing of waste tires as a root-zone medium for greenhouse crops. Two cultivars of zonal geraniums, `Danielle' and `Kim' were grown in media containing three grind sizes of rubber (10, 6, and 2.4 mm) and fiber from the fabric belting processed from waste tires in three proportions (1 rubber: 1 peat moss, 1 rubber: 1 vermiculite: 2 peat moss, and 2 rubber: 1 vermiculite: 1 peat moss, by volume). Two control media were also included: 1 vermiculite: 1 peat moss and 1 rock wool: 1 peat moss, by volume. The largest plants were grown in the 1 vermiculite: 1 peat moss medium, whereas the smallest plants were grown in the media containing the rubber grinds 2.4 mm and 6 mm making up 50% of the media. The media 1 rubber: 1 vermiculite: 2 peatmoss, regardless of grind or fiber, produced plants equal to the 1 rock wool: 1 peatmoss medium. All plants grown in media containing rubber by products had elevated levels of Zn and Cu in the foliage, but was greatest in media containing 50% rubber. Foliar P: Zn ratio was less for plants grown in media where rubber was 50% of the volume. The P: Zn ratio also was lower in plants grown in media with smaller grind sizes of rubber. Geranium plants can be successfully grown in media containing up to 25% rubber waste products without reducing plant quality.
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