Trial of Green Asparagus Out-of-Season Production for Establishing Year-Round Production in Kyushu, a Warm Area of Japan

Kyushu island, in southern Japan, is one of the main producers of green asparagus (Asparagus officinalis L.) in Japan, accommodating protected mother-fern culture in plastic greenhouses (PMC) as a conventional crop. In PMC, since few spears are produced from November to January, we attempted to produce spears during this period by prolonging the harvest of PMC to November and introducing “Fusekomi” forcing culture (FFC), in which rootstocks grown outdoors are transplanted into heated and/or thermal-retained culture beds in a plastic greenhouse in late autumn or early winter and spears are generally harvested for the following two or three months. In PMC, a combination of a foliage spray of Benzyladenine solution with thermal retention treatment in autumn prolonged the harvest period to the end of November without any significant decrease in yield the following spring. In FFC, rootstocks grown in the lowlands showed inferior spear productivity when transplanted into a greenhouse in late November, probably due to insufficient exposure to low temperature for breaking dormancy. In contrast, rootstocks grown in the highlands showed superior in productivity because they would be sufficiently exposed to low temperature for breaking dormancy by the time of transplanting. In lowlands, heating of greenhouses was unnecessary for FFC throughout the harvest period due to the mild winter climate. These results suggested that profitable year-round production of green asparagus without heating could be realized in Kyushu by combining PMC and FFC cropping types.