Truffle cultivation has quickly grown in Europe and elsewhere as a consequence of the increase in the demand of the market. Thus the optimization of the protocols for the production of elite mycorrhized plants are also needed, keeping in consideration the economic and environmental sustainability. The suitability of two compost-based potting mixes to produceQuercus pubescensWilld. plants mycorrhized with the black Périgord truffleT. melanosporumVittad. was tested as an alternative to the traditional potting mix used. The effects on mycorrhizal development and the morphometric assessment of the root and shoot system of theQ. pubescensseedlings were investigated eight months after the spore slurry inoculation in a glasshouse experiment. From the results obtained, the compost mix containing green organic residues from pruning and mowing (Mix 2) achieved better performance than the control and the potting mix based on composted municipal organic wastes, showing significantly higher mycorrhization percentage, root length, number of root tips, and root forks. In conclusion, a potting mix containing recycled green organic matter, which is readily available, cheap, and environmentally sustainable, can offer excellent mycorrhization performances and may be included in the mycorrhization process of downy oak seedlings withT. melanosporumunder controlled conditions.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12870-023-04194-y.