An atrium creates indoor conditions mimicing outdoor space. One effective method for creating outdoor-like conditions is landscaping using various plants. This study aims to provide building designers with daylight availability data for plants in atria. With the Daysim program, which uses weather data for Incheon, Korea, the daylight autonomies (DAs) of four-sided open-top atria for 112 cases were determined according to the geometry and orientation. The main geometric indices adopted were the aspect ratio (AR) and the plan aspect ratio (PAR). The results show that the DAs for 750 lx and 1000 lx were negligibly affected by the atrium shape, while the DA for 2000 lx was notably affected by the AR. The impacts of the PAR and orientation on the DA for 2000 lx were prominent in atrium wells with ARs of 0.36.