Testing new peat-free substrate mixtures for the cultivation of perennial herbaceous species: a case study on Leucanthemum vulgare Lam.

One of the major challenges for nursery growers is replacing peat with more sustainable materials that may also represent a worthy strategy to recycle organic refuse. Among organic matrices, coconut coir dust, green compost, and stabilized wood fibre are considered promising alternative to peat because of their suitable physical-chemical characteristics. These matrices were used to prepare substrate mixtures designed to achieve physical characteristics similar to those of the standard peat-based substrates usually adopted by growers (peat:pumice, 70:30 v v-1). An experiment was carried out in open field with Leucanthemum vulgare Lam., a plant species that could be used for ecological restoration, by using both the native and the ornamental variety of the same species (L. vulgare cv. 'Filigran'), the latter as test plants. Six different growing media were tested: i) peat:pumice 70:30 v v-1 (PP), used as commercial control; ii) coconut coir dust:pumice, 70:30 v v-1 (CP); iii) coconut coir dust:green compost 55:45 v v-1 (CGC); iv) coconut coir dust:stabilized wood fibre 60:40 v v-1 (CW); v) green compost:stabilized wood fibre 30:70 v v-1 (GCW) and, vi) coconut coir dust:green compost:stabilized wood fibre 40:30:30 v v-1 (CGCW). Plant biomass, biometric parameters, plant and matrix/substrate mineral content, and mineral composition of water drained out from pots were measured as main performance indicators of plants and growing media. All the tested peat-free substrates, with the exception of GCW, adequately supported plant growth and quality. Moreover, CP and CGCW improved some of the investigated biomass and biometric parameters compared with the control treatment. Substrates containing green compost were found to improve plant nutrition, because of the high availability of mineral elements in the raw material.