Mulch type could have different impacts on crops, especially in changing the root zone temperature (RZT) and microclimate around plants. The aim of research was to determine nitrogen rate and mulch type impact on watermelon early vegetative growth and RZT in order to single out the combinations with the most intensive watermelon vegetative growth in Mediterranean conditions. The split-plot field experiment was conducted during two years and included additional nitrogen rates (0, 60, 120 and 180 kg N ha^-1) and mulches (black PE-film, straw, bare ground). The most intensive watermelon vegetative growth can be achieved without additional nitrogen fertilization, only by mulching the soil with black PE-film or with the least rate of additional nitrogen (60 kg N ha^-1) and straw mulch. Due to environmental conservation, especially in karst regions, these combinations should be preferred over the combination with large rate of additional nitrogen (120 kg N ha^-1) and bare soil which had the equal growth intensity. Positive effect of black PE-film is the result of the highest values of RZT, i.e., accumulated heat (growth degree days – GDD) during the six weeks after planting. Although the maximum and mean RZT and GDD values below the straw were lower than on the bare ground, the positive effect of straw on vegetative growth can be explained by higher minimum RZT and better nutrient availability and utilization, due to other benefits of mulching such as better maintance of soil moisture and structure.