Growth Response of Photinia and Thuja and Nutrient Concentration in Tissues and Potting Medium as Influenced by Composted Sewage Sludge, Peat, Bark and Sawdust in Potting Media

Composted sewage sludge was blended with pumice and either bark, peat moss, or sawdust to form 6 potting media. Increasing the proportion of compost in media from 25 to 50% caused increased initial pH, electrical conductivity (EC), and airfilled pore space (AS) in all media, and increased growth of Photinia x fraseri Dress. and Thuja occidentalis L. ‘Pyramidalis.’ Sawdust-containing media had the highest pH, EC, and AS; sphagnum peat-containing media the highest water holding capacity and greatest shrinkage; bark-based media the highest bulk density. Plant growth in compost-based media containing peat or bark was equal to or better than that in two commercial media composed primarily of bark or peat.