A single cropping system with 1-year-old rootstocks by forcing culture has been proposed for white asparagus (Asparagus officinalis) production in Japan. To develop a method to control the sprouting period for such a cropping system, we investigated the effects of low oxygen (O2), high carbon dioxide (CO2), and a combination of these on the sprouting of asparagus spears, using a laboratory-scale test. We stored the rootstocks without soil for 6 weeks in six treatment conditions (20% O2, control; 20% O2 + 8% CO2; 20% O2 + 16% CO2; 8% O2; 8% O2 + 8% CO2; and 8% O2 + 16% CO2). After storage, we planted the rootstocks in pots with soil and investigated their yield performance for 20 weeks. Only the 8% O2 + 16% CO2 treatment applied during rootstock storage suppressed the sprouting of spears. The number of harvested spears and the yield of spears per plant in the 8% O2 + 16% CO2 treatment was higher than in control at the 16-20-week period, although the weight per spear did not differ. We suggest that the extension of sprouting after planting was due to the suppression of sprouting during rootstock storage. Our results suggest that controlling atmospheric O2 and CO2 concentrations around the rootstock during storage could be a new, effective method to alter the harvest period of white asparagus, including cultivation of fresh asparagus in a single cropping system with forcing culture.