The 18 RUSTICA biochars were grouped based on the main elemental composition in three groups. These were1) the Woody biochars which consisted of biochars made from Apple clippings, Pear clippings, Almond tree clippings, Pistachios clippings, Olive tree clippings, Pinot and Cabernot Sauvignon wine clippings and Kiwi plant clippings; 2) Shells and husks which were made from Cocoa pods, Cocoa shells and Coconut husks and 3) the highly fertigated from fertigated crops which consisted of sweet pepper and egg-plant stems and leaves (residues after harvesting). Only for the highly fertigated feedstock, leaching tests are necessary to avoid high instant salinity in a fertilizer mixture. Based on these, it was concluded to only use 10% of the highly fertigated feedstock in a woody feedstock mix for plant trials. The variation in fertigating elements in the woody feedstock could be neglected and hence gives a high degree of freedom for bulk volumes and easier logistics.