The effect of a 25% addition of composted pig slurry on the rooting of Pelargonium peltatum hort. in a greenhouse medium consisting of perlite and highmoor peat (1:1 v/v) has been studied. The purpose of this paper is to define relationships between the rooting process and occurrence of microflora in the media without compost (control) and with the addition of that manure, as well as in the rhizosphere of the rooted plants. The development of whole bacterial communities determined by their biomass size (direct method) and the number of colony forming units (CFU) of actinomycetes and fungi (on selective media) were estimated. The compost added to the greenhouse medium stimulated the rooting of geranium cuttings significantly, increasing their root length by almost 80% and root biomass by over 40%. It also affected a 35% increase in shoot biomass. Except propagative forms of fungi, the medium enrichment with compost simultaneously intensified microflora development, which appeared to be particularly evident in the case of actinomycetes, which belong to bacteria producing phytohormones; the number of these microorganisms in the rhizosphere of plants rooted on the medium with compost was twofold higher than on the medium alone.