Zeolite tuff deposits located in the sedimentary basins of Orestias and Ferres-Alexandroupolis, Evros County, Greece are studied to determine their suitability as hydroponic substrate, used various mineralogical and chemical techniques. Large bodies of greenish to yellowish, massive zeolitic tuffs occur in the Metaxades, Pentalofos, Twin Hills and Palestra areas of Orestias basin as well as in Makrylofos, Doriskos and Kavissos of Ferres-Alexandroupolis basin. The zeolite tuff deposits of Ferres-Alexandroupolis basin consists mainly of clinoptilolite and mordenite assemblages, accompanied by silica polymorphs and feldspars. Contrary, the zeolite tuffs of Orestias basin are very rich in clinoptilolite or heulandite (Metaxades deposit), whilst mordenite is almost absent. The tuffs from Pentalofos and nearby Twin Hills and Palestra areas are extremely rich in clinoptilolite, reaching 90% of the total mineral content, while 10%, is represented by cristobalite and/or feldspars. All the zeolite tuff deposits studied had high cation exchange capacity and almost neutral pH. The non-dependence of the ion exchange capacity to different particles size could be prove beneficial in hydroponic cultivations, as particles of large grain size may be used without any effect on the quality of the material. The tuffs contain exchangeable potassium, calcium and magnesium, and, therefore, certain plants could use them as a source for these elements. Although zeolitic tuffs of the Doriskos-Kavissos area have high Cation Exchange Capacities (CEC), the presence of chlorine ions, as well as large quantities of exchangeable sodium might lead to toxicity of plants grown in such substrates. The Metaxades tuffs display the lowest CEC of all the Greek samples examined. The Palestra-Pentalofos zeolite tuff deposits combine: high CEC, absence of chlorine ions and relatively low exchangeable sodium. The parameters above make most of the tuff deposits studied suitable for use in hydroponics.