The aim of this investigation was to evaluate solid digestate as a growing substrate for plug seedlings. Four mediums prepared from solid digestate, vermiculite, perlite and activated carbon were used to determine optimum growing substrate for tomato seedlings (Zhongshu six). The substrate used in this study mixed as solid digestate: vermiculite: perlite: activated carbon were (m:m): 4:13:2:1, 8:9:2:1, 12:5:2:1 and 16:1:2:1, respectively. Besides, peat: vermiculite of 2:1 (v:v) was used as the control. Various seedling indices were measured to assess the quality of the substrates. Tomato seedlings grown in solid digestate: vermiculite: perlite: activated carbon of 16:1:2:1 (m:m) displayed the best quality compared with all the other treatments, due to a correct balance between the digestate nutrient supply and the physical properties provided by vermiculite, perlite and activated carbon. Solid digestate could be a potential alternative for plug seedlings.