Quality of compost is divers, and measurement of compost characteristics can help to estimate the fitness of a compost for the intended use. Especially compost maturity is important in case of high compost:soil ratios. In this study, it was verified how compost:soil ratios affect growth of garden bean Vicia faba, and what compost characteristics determine the fitness of compost for plant development. Four agricultural waste composts with varying characteristics were mixed with soil at 0, 10, 30, 50 and 100 volume percentage. Characteristics of the mixtures could be well estimated from the weighted mean of the pure soil and compost characteristics. Garden bean growth in these mixtures was monitored during 5 weeks. Final plant biomass was larger when 10% compost was added, compared to pure soil. Also plant K content increased by compost addition. At 50% and 100% compost, plant biomass decreased or even became zero depending upon the compost. Compost EC and nutrient content showed positive correlations with plant biomass at 10% compost additions, but negative correlations at 30% compost addition. Relatively small compost doses have positive effects on plant growth, whereas larger additions can have negative effects, possibly related to salt stress. Compost C/N ratio, often used as maturity characteristic, turned out not to be a good indicator of the fitness of compost for plant growth.