Urban green infrastructures have been extensively studied for their ability to mitigate the urban heat island (UHI) effect. However, allotment gardens (AGs)—a prominent type of urban green infrastructure within many European cities—have not yet been comprehensively investigated concerning their microclimates. In this study, nocturnal air temperatures ( $T_N$ ) in 13 AG complexes (AGCs) were measured during the summer of 2018 in Berlin, Germany. These were compared to measurements in densely built-up urban areas (URB), two large inner-city parks and rural areas (RUR). On average, the assessed AGCs were 2.7 K cooler at night than URB. Most of the investigated AGCs (11/13) displayed a larger mean $T_N$ difference to URB ( $\overline{\Delta T_{N AGC} }$ ) than the examined urban parks. RUR showed the largest differences to URB ( $\overline{\Delta T_{N RUR}}$ ), indicating a UHI effect. Furthermore, the influence of land surface characteristics of the AGCs on $\overline{\Delta T_{N AGC}}$ was analyzed. $\overline{\Delta T_{N AGC}}$ decreased significantly as the floor space index around AGCs increased. The analysis of the shape complexity also produced a significant positive correlation with $\overline{\Delta T_{N AGC}}$ . In contrast, size and distance to the city center of an AGC decreased significantly with increasing $\overline{\Delta T_{N AGC}}$ . This study provides first insights into the microclimate of AGs and influencing variables concerning $T_N$ .