This study aimed to evaluate the effect of different types of shading nets used as undercover of plastic in greenhouses of hydroponic cultivation of lettuce. The experiment was performed in greenhouses covered with plastic film of 150?μm with three types of undercover nets: thermal reflector net, black, red and acontroltreatment - without the use of the undercover.To evaluate the environmental changes caused by treatments thermohygrometer data logger swere installed in each greenhouse as well asone in the external environment. The devices recorded the air temperature every 15 minutes from May 18th2011to June 14th2011. By using these data, it was possible to estimate the values of the growing degree-daysineach environment. To analyze the changes in plant growth and development caused by the treatments, five samples were taken along the experimental period. Inthe laboratorywe counted the number of leaves greater than 10cmof lengthand measured the leaf area index. The results indicated that the use of the nets changed the overall patterns of temperature and relative humidity. The use of thermal reflector net and black net reduced the maximum temperature at 4.7 and 3.6?°C, respectively, compared to the controlalso allowing for lower growing degree-days at the end of the experimental period.As for the morphological changes caused by treatments, we observed that the use of thermal reflector netand black net increased the number of leaves greater than 10cm andalso the leaf area index.The use of black net or thermal reflector net as undercover in greenhouses can be a feasible alternative to increase the production of lettuce in tropical conditions
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