The potential of herbage composts as horticultural substrate and source of nutrients was investigated. The effect of botanical composition of the herbage, as well as the effect of different kinds and amounts of carbon sources, on nitrogen losses during composting and growth properties of the compost were studied. Growth tests with different plant species as well as chemical analyses of total- and easily-soluble plant nutrients were used to evaluate compost quality. Seven herbage composts were studied and used in growth tests with seven different test plants. The results were evaluated by conventional and multivariate statistical methods.