Using several different ericaceous ornamental species, we compared the growth, mineral nutrition, and composition of plants in response to growing media amended with varying proportions of sphagnum moss peat (peat) or coir dust (coir). Plants were grown for 16 weeks in media consisting of 80% composted Douglas fir bark with 20% peat, 20% coir, or 10% peat and 10% coir. Sixteen weeks after planting, decreases in extractable P were larger in peat-amended medium than the coir-amended medium, while decreases in extractable NH4-N and NO3-N were larger in the coir-amended medium. In general, leaf and stem dry weight, the number of leaves and stems, and total stem length increased with increasing proportion of coir in the medium while root dry weight either increased (Kalmia latifolia), decreased (Rhododendron, Gaultheria), or was not influenced by increasing the proportion of coir in the medium. The composition of the growing medium also influenced aspects of plant marketability and quality including: leaf greenness (SPAD), plant form (e.g., number of leaves per length of stem), and partitioning of biomass (e.g., root to shoot ratio). Nutrient uptake and fertilizer use was significantly different between the media types. Depending on the cultivar, we found that the coir-amended medium resulted in higher uptake or availability of several nutrients than peat-amended medium. Up take or availability of N, P, K, Ca, and S was enhanced for several cultivars, while uptake or availability of Mg, Fe, and B was similar between media types. Most cultivars/species growing in the coir-amended medium had higher production or accumulation of proteins and amino acids in stems than plants growing in peat-amended medium, while the production of proteins and amino acids in roots was lower in plants growing in coir-amended than in peat-amended medium. For the cultivars/species we tested, coir is a suitable media amendment for growing ericaceous plants and may have beneficial effects on plant quality.
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