Mounding, also known as earthing up, is widely carried out at any time during the growth cycle of Vigna subterranea (L.) Verdcourt, viz. bambara groundnut – a species with underground pod setting – by subsistence farmers throughout Africa. This agricultural practice consists of bringing soil to the crown of bambara groundnut plants and has been shown to improve seed yield of the crop. However, little information exists if and how the timing of mounding affects the productivity of the crop. To address this, two experiments during two consecutive years in rainfed fields in the Sudan–Sahel agro-ecological zone of Burkina Faso were conducted. Yield data confirm the findings from a drier part of Burkina Faso; i.e., mounding of bambara groundnut should not be carried out around the time of flowering. In a semi-arid area, such as Sudan–Sahel agro-ecological zone and with germplasm maturing within 90 days after sowing, mounding should be done early (about 2 weeks after sowing, WAS) or late (7 WAS) but not at 4 WAS, which coincides with the flowering period, as it reduces bambara groundnut seed yield.