Azaleas, Rhododendron indicum L. ‘G.G. Gerbing’, were transplanted into landscape beds amended with yard waste compost at rates of 0, 5.1, 7.6, or 10.2 cm (0, 2, 3, or 4 in) incorporated into the top 18 cm (7 in) of a sandy soil. Plants were irrigated on alternate days (high irrigation rate) or on every third day (low irrigation rate), and shoot and root growth measurements were recorded at 0, 4, 8, 12, and 18 months after transplanting. Differences among compost treatments for plant quality and root elongation were observed after 8 months. By 18 months, incorporation of 7.6 or 10.2 cm (3 or 4 in) of compost resulted in plants with larger shoots, greater root, elongation, and larger root masses compared to the 0 and 5.1 cm (2 in) compost treatments. The larger azalea shoots and roots achieved with high rates of compost occurred under both irrigation regimes. Incorporating 7.6 or 10.2 cm (3 or 4 in) of compost increased root elongation, mostly between 4 and 8 months, and increased root mass after 12 months. Compost incorporation affected the quality of plants under high irrigation, with 10.2 cm (4 in) of compost producing the highest-quality plants.

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Author notes

This research was supported by the Florida Agricultural Experiment Station and a grant from Enviro-Comp, Inc. and approved for publication as Journal Series No. R-08149.

2Associate Professor and Biological Scientist, respectively