Peat-Free Composted Bark and Wood Fiber Blends for Container Ornamentals: Species-Dependent Growth and Quality Responses

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Identification of environmentally sustainable alternative materials or material blends capable of effectively replacing peat in ornamental horticulture is a significant global challenge. The present study involved five separate experiments with three growing media treatments consisting of two composted bark and wood fiber mixes (at 80:20 and 60:40; bark:wood fiber) and pure peat as control. Five different ornamental plants, namely Leptospermum scoparium ‘Martinii’, Carex morrowii ‘Everglow’, Cotoneaster frigidus ‘Cornubia’, Viburnum tinus ‘Eve Price’, and Hypericum × hidcoteense ‘Hidcote’, were evaluated during the study. Results revealed that all the plant species performed well and produced higher aesthetically ranked plants in the two bark mixtures as compared to control (peat), except Leptospermum scoparium ‘Martinii’. The same bark mixes (80:20 and 60:40; bark:wood fiber) produced significantly higher biomass than peat for Viburnum tinus ‘Eve Price’ (>53.9%) and Hypericum × hidcoteense ‘Hidcote’ (>17.7%), while for Carex morrowii ‘Everglow’ and Cotoneaster frigidus ‘Cornubia’, the bark mixes were comparable to peat. However, Leptospermum scoparium ‘Martinii’ peat produced significantly higher biomass than the bark mixes. These bark mixes produced more biomass than peat under Viburnum tinus ‘Eve Price’ and Hypericum × hidcoteense ‘Hidcote’ even though the peat had significantly higher pre-planting mineral nitrogen (>×2.29) and available phosphorus (>×1.54) than the bark mixes. These results show that composted bark and wood fiber growing media can effectively be used as an alternative to peat for the woody ornamentals and sedge species tested, although responses were species-dependent.