Abstract: The invention relates to a method of producing plants mycorrhyzated (i.e. having their roots associated) with symbiotic fungi, so as to apply mycorrhyzation to already adult plants and obtain mycorrhyzated plants which can produce fruit-bearing bodies immediately after being planted.The method consists in cultivating a set of young plants in sterile soil, preferably starting from seed, and in mycorrhyzating the young plants grown in sterile conditions, by placing their roots in contact with roots previously mycorrhyzated with the desired fungus and obtained under natural conditions from other plants. The resulting pilot young plants are planted in a sterile greenhouse or sterile nursery, in which already adult plants are subsequently planted so as to be mycorrhyzated, after secondary roots have first been eliminated and the remaining roots have been sterilized. The pilot young plants mycorrhyzate the adult plants with the desired fungus, so that the plants can immediately produce fruit-bearing bodies.