Abstract: Microporous, fertilizing materials or compositions, retaining water and accelerating the germination and growth of plants, characterized in that they are composed of a hydrocarbon base containing asphaltenes modified by an oxidation agent producing a liberation of gas, directly, or indirectly, in combination with at least one mineral compound reacting in acid medium, to which materials or compositions it is possible to add, by simple mixing, appropriate common manures, oligo-elements and fertilizers.Method of preparation of fertilizing materials or compositions, characterized in that a non-acid oxidizing agent is mixed with a molten hydrocarbon base in a proportion of 25 to 50% by weight with 5 to 10% of a mineral compound, the mixture is kept for 5 to 7 hours at 180.degree.-250.degree. C., poured into metal trays, cooled, ground and screened into granules of a diameter ranging from 1 to 3 mm.