Evaluation of compost and anaerobic digestion residues as a component of growing media for ornamental shrub production

For some decades, compost has been investigated as a partial substitute for peat in the preparation of pot growing media. Nevertheless, its use for the preparation of professional substrates still remains limited. Anaerobic digestion residues are agro-industrial by-products that have recently gained interest due to their potential as feedstock for growing media preparation. In this study, 8 growing media: peat blended with 4 rates (0, 15, 30 and 45% v/v) of green waste compost and two rates (0 and 20% v/v) of anaerobic digestion residues were evaluated. After physical and chemical characterization, the 8 media were used to grow rooted cuttings of Rosa 'Sweet Haze' and Abelia ×grandiflora 'Prostata' in 15 cm diameter plastic containers. One year old abelia plants, grown in a peat-based media in 15 cm containers, were also re-cultivated in 19 cm containers using the prepared substrates. Results showed that increasing compost rates increased bulk density, pH and electrical conductivity, but reduced organic matter, total pore space and air filled porosity. Addition of anaerobic digestion residues limited the increase of these parameters. Response of plants differed according to species and, for abelia, type of cultivation. Roses grown in the substrates with compost were similar to those grown in peat media. On the contrary, abelia plants from cuttings were negatively affected by increasing rates of compost. However, addition of anaerobic digestion residues to the substrates improved plant growth. Plants of abelia repotted in 19 cm containers were less negatively affected by compost than abelia cultivated in 15 cm container and, in general, only at the highest rate, and growth was promoted by the addition of anaerobic digestion residues. © 2017, International Society for Horticultural Science. All rights reserved.