Recent concerns over the environmental impact of peat harvesting have led to restrictions on the production of peat based potting substrates. Therefore the objective of our study was to evaluate the use of compost and biogas residues without and each with 20% additives (Perlite, Styromull, Hygromull, Lecaton, Peat, Cocofiber) as a substitute for peat. Ryegrass (Lolium perenne L.), chosen as an experimental plant, was cut four times. The results reveal that compost and biogas residues are suitable potting substrates. The incorporation of additives mixed into the basic materials partly resulted in higher yield and nutrient uptake. However, the difference among additives was mainly insignificant. Incorporation of Hygromull, especially into biogas residues favored plant growth and increased the uptake of nutrients, which is attributed to the fact that Hygromull stores nutrients and delivers them even later in the growing season. Furthermore Hygromull reduces the salt concentration of the medium, resulting in favored plant growth of younger plants.

Composting has been considerably recognized as a viable management method for solid organic wastes aimed at recycling of its end-product as a potting substrate for ornamental plants. Pelargonium and Salvia as salt-sensitive plants were grown in the mixture of compost (75, 50, 25% by volume) and additives (Hygromull, Cocofiber and SPS-standard soil type 73 with 70% peat and 30% clay). Since plants may suffer from a high salt content, thus in a further experiment compost was added as a partial substitute for peat. The results of the first pot experiment reveal that the large percentage of compost in the substrate had negative effects on plant growth and nutrient uptake (N, P, K and Na). Both yield formation and nutrient uptake significantly increased and almost gained levels of those in the control in the second pot experiment when plants were grown in peat-based substrates. Especially, the growth of Salvia was significantly improved. Consequently, the compost-based media (> 50% volume of compost) cannot be recommended for salt sensitive ornamental plants, while less than 25% of compost incorporated into peat creates peat-based substrates which reasonably enhanced growth of Pelargonium and Salvia.