Purpose Food security is threatened by increasing soil degradation; thus, it is imperative to reclaim and amend the degraded soil. Multifunctional wood vinegar and biochar pyrolyzed from waste biomass are proposed as highly promising soil amendments. However, there is still a knowledge gap on the cooperative performance of wood vinegar and biochar in affecting plant growth in agricultural production. Material and methods Waste trunks of poplar-derived wood vinegar (PWV) and biochar (PBC) were produced using slow pyrolysis simultaneously at 500 degrees C for 5 h. Two common vegetables, pepper (Capsicum annuum Linn) and tomato (Lycopersicon esculentum Miller), were selected to investigate their responses to PWV addition using a germination experiment and the individual and co-application of PWV and PBC using a 30-day pot experiment. Results and discussion The addition of PWV had no effects on the germination of pepper and tomato, while it promoted the lengths of the root and shoot at low concentrations (e.g., 0.002% and 0.02%). Additionally, PWV individually promoted the root development of pepper seedlings, such as the root length by 45.4-51.6%, and increased the biomass of the shoot and root by 20.9-22.0% and 100-113%, respectively; however, co-application showed little effects. For tomato, PWV individually exerted little influence on its growth, while PBC individually facilitated its seedling growth, including root development and above ground and underground biomass production. Compared to the individual application of PWV, the co-application of PWV and PBC significantly increased the root length, surface area, and volume of tomato by 98.0%, 66.7%, and 83.1%, respectively. These results could attribute to the enhanced nutrient availability and the slow-released active acid and phenol components in PWV adsorbed by the PBC. Conclusions The individual application of PWV or PBC stimulated pepper seedling growth, whereas the co-application of PWV and PBC more efficiently stimulated tomato seedling growth than did the individual application. These findings provide valuable information on the co-application of wood vinegar and biochar to enhance crop growth, which is useful for improving soil health and food security.