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The suppressive ability of three plant residue-based composts that could serve as components of soilless media for several vegetable crops was tested on four different formae speciales of Fusarium oxysporum: melonis, basilici, radicis-lycopersici and radicis-cucumerinum. The composts were prepared under controlled conditions from a mixture of separated cow manure (SCM) with orange peels (OP), wheat straw (WS), or dried tomato plants that had been removed from the greenhouse after the end of the season (TP). Disease development in melon, tomato and cucumber seedlings growing in the three composts was significantly less than that observed in peat. Plant inoculation was achieved by conidia produced in culture, conidia naturally produced on infected stems and soil inoculum produced by enriching the soil with infected tissues. Pathogen colonization of the roots and stems of infected melon plants grown in TP-SCM and OP-SCM composts was significantly lower than that of peat-grown plants. Sterilization by gamma irradiation reduced the suppressive capability of TP-SCM and OP-SCM composts, whereas it did not affect the disease development and final disease incidence in peat. Tested formae speciales exhibited differing decline rates of the conidia incorporated in the composts, compared with the rate in the peat control, which suggests that different mechanisms may be involved in the suppression of the different pathogens. The present study shows that composts based on plant-waste residues suppress diseases caused by different formae speciales of Fusarium oxysporum.