The use of solar flat plate collectors for heating agricultural greenhouses has proved to be interesting. Their efficiency depends at the same time upon the ambient climatic conditions and the thermal performances of solar collectors. In this study, we present the thermal results relative to the effect of the heater system on the microclimate greenhouse and the agronomic results of the greenhouse culture of melon. These results are of a big interest because, compared to a unheated greenhouse, a precocity of 14 days has been obtained, and a high homogeneity of melon grades has been observed. We also notice that, for the same density of plantation, a very good gain average in weight per plant has been recorded in the heated greenhouse.