Anaerobic digestate has been commonly used for the cultivation of vegetable seedlings and as one of the measures for improving the peat-substrate. Studies have shown the influence on aromatic plants, and leafy vegetables, but no further research about the effect on greenhouse vegetables. The main objective was to investigate the effect of the additional insertion of different rates of solid grain waste digestate in the peat-substrate on tomato seedling quality. The research was carried out in a greenhouse covered with double polymeric film at the Institute of Horticulture, Lithuanian Research Centre for Agriculture and Forestry. Two factors were investigated: seedlings establishment method (transplanted and direct sowed in the pod seedlings) and different substrates: control (peat), peat +10% digestate, peat+20% digestate with 3 repetitions by using a completely randomized design. The biometrics and photosynthetic parameters of the seedling were evaluated. The results showed that 10 % of solid grain waste digestate application with transplanted seedlings had a significant effect on plant height, leaf number, leaf area, and all plant fresh mass of tomato seedlings compared with the control variant. Photosynthetic parameters such as photosynthetic rate and transpiration rate of transplanted seedlings with 10 % digestate application were also higher. Transplanted seedlings with a 20 % rate of solid grain waste digestate showed the increase leaf chlorophyll index and nitrogen balance, but not in biometrics of the seedlings, and their photosynthetic parameters showed no significant difference between other variants. The use of different solid grain digestate rates can increase tomato seedling biometrics and photosynthetic parameters. The research showed that all transplanted variants of tomato seedlings have better biometrics and photosynthetic parameters comparing with direct sowed in the pod seedlings.