Biomass production and reproductive performances of native and ornamental herbaceous plants in peat-free growing media

Green sustainability is becoming more and more an issue in the management of urban greening. Accordingly, the use of native species of wild flora is increasing in urban greenspace design and restoration ecology because of their capacity of adaptation to adverse local environmental conditions and support long-term persistence of ecosystem recovery. Although the use of peat-free growing media is increasing in professional nursery, due to the environmental concerns around peat bogs exploitation, the use of materials suitable to replace peat in the growing medium is poorly investigated for the production of wild plants. In this work, we investigated the biomass production and the reproductive performances of eight native species (Agrostis stolonifera, Carex pendula, Dianthus carthusianorum, Iris pseudacorus, Leucanthemum vulgare, Lychnis flos-cuculi, Lythrum salicaria and Scabiosa graminifolia) and two ornamental species (Deschampsia caespitosa and Verbena bonariensis) in four different growing media (peat:pumice 70:30 v/v as a control; coconut coir dust:pumice 70:30v/v; coconut coir dust:green compost 55:45 v/v; coconut coir dust:green compost:stabilized wood fibre 40:30:30 v/v). Biomass accumulation and biometric indicators were assessed during blooming period, by measuring above-ground biomass, below-ground biomass, total biomass and, for a subset of species, number of flowering stems and number of flowers. Whilst plants grown in green compost and coconut coir dust media generally tended to have same biomass and comparable reproductive performances of plants grown in peat-based medium (with only one exception; i.e. Verbena bonariensis), plants grown in wood fibre media showed lower biomass accumulation, although not always (not all species) statistically significant. Green compost and coconut coir dust represented excellent substitutes of peat for the cultivation of native herbaceous plants in commercial nursery.