The advantage of the high passive cooling effect of traditional extensive green roofs during daytime is always offset against their disadvantage of the high thermal insulation effect during nighttime in summer in subtropical regions. The purpose of this study was to develop types of green roofs that can not only improve the passive cooling effect of extensive green roofs during daytime but also mitigate the thermal insulation effect of extensive green roofs during nighttime in summer in humid subtropical regions to reduce the cooling energy load over 24 h compared with that of traditional extensive roofs. The following factors were considered to obtain such an ideal extensive green roof-the depth of growth medium, the proportion and placement of lightweight expanded clay aggregate (LECA), and the presence and absence of a non-CAM edible plant. The results indicated that, compared with the 0% LECA (traditional garden soil) roof without plants in the second stage and under a slightly different air temperature (0.26 degrees C during daytime and 0.57 degrees C during nighttime), the introduction of Ipomoea batatas and 10%-40% LECA can significantly increase the passive cooling effect by approximately 1.5 times (5.51-6.21 degrees C) during daytime and significantly mitigate the thermal insulation effect by approximately half (2.05-3.20 degrees C) during nighttime. In summary, the introduction of Ipomoea batatas (non-CAM edible plant) and LECA into the traditional extensive roofs can effectively reverse the higher-cooling-and-stronger-warming effects to higher-cooling-and-weaker-warming effects.