After mushrooms are harvested a large amount of used compost that has a high content of organic matter and the rich mineral composition remains. Such accumulated compost is a good material to improve the physical properties of soils and plant nutrition. The aim of this study was to investigate the possibility and feasibility of using spent mushroom compost from Agaricus bisporus as an alternative growing media for greenhouse production of Pelargonium peltatum L. and Petunia hybrida Juss. seedlings. The experiment was conducted under greenhouse conditions at the Faculty of Agriculture, University of Banja Luka (Republic of Srpska-RS, Bosnia and Herzegovina-BiH) in 2014. It was arranged in a split-plot design with four replicates and two treatments (commercial substrate and mixture of commercial substrate and spent mushroom compost) for each variety. Morphological parameters, were recorded regularly during growth and development of seedlings. At the end of experiment, seedlings were sampled and root and above-ground fresh and dry weight were recorded. Obtained results showed significantly higher values of all investigated parameters of seedlings grown on spent mushroom compost. Thus it can be concluded that use of spent mushroom compost, as additional of commercial substrate in the production of geranium and surfinia seedlings is possible and economically justified as well as environmental friendly.