ABSTRACT Containerized ornamental plant production is facing several environmental challenges. One of them is to replace the widely used, but with questionable sustainability, peat based substrates and another is to avoid water contamination by chemicals leaching from the nursery. Therefore, as have been verified that petunia and pelargonium plants can be produced in peat-based growing media partially replaced by vermicompost (V) and biochar (B) without decreasing commercial quality, this study has focused on analyzing the leachate from a standard peat-based substrate as a control, used for producing these two ornamental species, and those from the same substrate to which different proportions in volume of V (10% and 20%) and B (4% and 12%) have been added. The amount of nitrogen leached from the mixed substrates was reduced compared to the control one in both species (on average 37%). Nitrogen was leached mainly as nitrate-nitrogen (89% in Petunia and 97% in Pelargonium). In Petunia phosphorous leaching was also decreased (30%) for the treatment with 10% V and 4% B, while potassium leaching in substrate containing 20% V and 12% B increased by 100%. Our results show that these two organic materials tested (V and B) can help producers to reduce the use of peat and chemical fertilizers as well as the risk of contamination by chemicals, mainly nitrate.