The tropical grounds show great restrictions for tree production after they have been used and over-exploited by man. A strategy to increase the levels of production is based on the fertilization according to the requirements of the trees. As mycorrhization is a biological low cost alternative that can contribute to the success of the reforestation, we wanted to establish how it was possible to favor the surviving and growth of arboreal species in green houses by means of the quantification of mycorrhizal fungi using ground samples in the species Tabebuia rosea and Cordia alliodora in different localities from Costa Rica, Central America.Samples in ten different sites were analyzed and the quantification of spores was made by sifting. The percentage of colonization by roots was considered at microscopic observation by roots according to methodology of Sieverding. The results obtained in this investigation concluded that from the variety of the present sorts of Micorrizas Vesiculo Arbusculares in the ground sample those that demonstrated better behavior with Tabebuia rosea and Cordia alliodora were Glomus sp. and Gigaspora sp. In addition, to obtain a greater growth and development of the trees, it is necessary to favor the mycorrhizal population in the plants within their first days of birth.