Humic-like substances (HS*) extracted from six different digestates were used for the biostimulation of hydroponic culture of Lactuca sativa. A preliminary dose-screening trial was performed with the application of extracts from two digestates (from sewage sludge and manure) and a commercial reference of HS* from leonardite. In this test, the application of extracts from digestate performed statistically better than a commercial reference when compared to the blank. The preliminary study has confirmed the interest of extracting HS* from digestates for application as biostimulants in hydroponic systems. The full-test with the extracts from six different digestates is being carried out for 3 months and will include aerial and root biomasses and root architecture assessment.