In Japan, white asparagus is produced by blanching with soil mounds or film-cover shading methods. However, with either method, white asparagus is produced only in the spring and not during the winter months, when labor and facilities can be more effectively utilized. Recently, a forcing-culture method for green asparagus using polyethylene bags was developed to reduce the workload required in green asparagus production during winter. In this study, we selected a medium composition that reduces bag weight while maximizing yield under a white asparagus forcing culture, as well as cultivars with superior yield and quality. In the first experiment, asparagus was cultivated under forcing culture in polyethylene bags using three different mixed-composition media: lightweight media and horticultural media (1:1, v/v), lightweight media and bark compost (1:1, v/v), and horticultural media and bark compost (1:1, v/v), comprising lightweight media with a bulk density of 0.45 g·mL−1, horticultural media with a bulk density of 0.8–0.9 g·mL−1, and bark compost of 0.4 g·mL−1. The lightest bag (weighing 8.0 kg) contained a combination of lightweight medium and bark compost. No differences were observed between the three combinations in terms of asparagus growth, yield, or spear weight. In the second experiment, the cultivars ‘Taihowase’, No. 056, ‘Suguderu II’, and ‘Welcome’ were grown in a combination (1:1, v/v) of lightweight medium and bark compost. The spear weight of No. 056 was greater than that of ‘Welcome’. No differences in sugar content were observed among the four cultivars. The protodioscin content of ‘Suguderu II’ was higher than that of ‘Taihowase’, No. 056, and ‘Welcome’. These results indicated that forcing culture using bags is practical and that a combination of lightweight medium and bark compost is suitable for this culture method. The best asparagus cultivars among those tested were No. 056, which produced heavy young stems, and ‘Suguderu II’, which developed spears with a high protodioscin content.
View full abstract