Use of Spent Mushroom Substrate for Growing Containerized Woody Ornamentals: An Overview

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Abstract
There are substantial environmental and economic benefits to be gained by recycling spent mushroom substrate (SMS). Researchers throughout the world have grown many types of crops with SMS but information with ornamental nursery crops is sparse. High salt levels in SMS is largely responsible for its restricted use in agriculture. Investigations showed that many ornamental woody species grew well in 6-liter (2-gal) regular nursery containers amended with different proportions of SMS (33%, 67%, and 100% by volume) mixed with bark. Test species were: cotoneaster (Cotoneaster dammeri ‘Coral Beauty’); deutzia (Deutzia gracilis); dogwood (Cornus alba and C. alba ‘Argenteo-marginata’); forsythia (Forsythia × intermedia ‘Lynwood’); juniper (Juniperus sabina ‘Blue Danube’ and J. virginiana ‘Hetzii’); ninebark (Physocarpus opulifolius); potentilla (Potentilla fructicosa ‘Red Ace’); privet (Ligustrum vulgare); rose (Rosa ‘John Franklin’); and weigela (Weigela ‘Bristol Ruby’ and W. florida ‘Variegata Nana’). Despite variable species response, there was little relationship of growth performance to: source of SMS (different farms, fresh or aged, leached or unleached); initial or subsequent salt levels in the media; chemical or physical characteristics of the media, including increasing shrinkage with increasing amounts of SMS; or contents of leaf nutrients. Plants of all species, except privet, achieved marketable size and quality at harvest. Time-course studies demonstrated that rapid leaching of undesirable high salt levels from the containers was the key to our successful results. In further studies which evaluated a wider range of amendment combinations (peat, bark, and sand) with SMS included in amounts (25% or 50%) more desirable in commercial container nursery practice, all SMS amended media promoted excellent growth of nursery crops. Minimal shrinkage was obtained with a medium consisting of 25% sand, 25% SMS, and 50% peat or bark.