Fusarium wilts, caused by the fungus Fusarium oxysporum, are important diseases of horticultural and agricultural crops and lead to significant yield losses. The pathogen infects the roots and colonizes the vascular tissue, leading to wilting and finally death of the plant. The objective of this study was to investigate the efficacy of amendment of green compost and a Trichoderma hamatum strain against Fusarium wilt of radish. The substrate effects and the effect of a Trichoderma strain were tested in a potting soil bioassay. The tested composts lowered the disease level and had a positive influence on the plant yield (fresh weight and dry weight). Nothwithstanding, only a small dosis effect of the amendment was observed. In the presence of the tested Trichoderma hamatum strain no significant lower disease level was observed. Furthermore, a minor effect on plant yield (fresh weight and dry weight) was observed compared to the amendment with only green compost. Maybe the pathogenic Fusarium oxysporum strain and the Trichoderma strain competed for nutrients, iron could be a limiting factor. One possible approach to improve biological control may be the application of combinations of biocontrol agents.