Asparagus has traditionally been cultivated in the open field in Japan, mainly in districts with relatively cool weather (Hokkaido and Nagano Prefecture). Asparagus production increased in the 1970's and 1980's in Japan. But the overall planted area and yield gradually decreased, especially in production areas such as Hokkaido Prefecture. Moreover, imports of fresh asparagus increased after 1990. The amount of imported fresh asparagus was 22,700 t in 1995, which was approximately equal to the domestic output (23,400 t) of Japan. The frequency of imported fresh asparagus was 31% in the Tokyo Central Wholesale Market in 1990. It reached 48% in 1995, and the amount of imported fresh asparagus increased every month. On the other hand, in the Osaka Central Wholesale Market, though the percentage of imported fresh asparagus was 32% in 1990, the percentage of imported fresh asparagus did not increase because that of domestic fresh asparagus increased except for January to March. This was because harvest time was extended by the establishment of the mother stalk method for long-term and greenhouse cultivation in the southwestern part of Japan, which is close to Osaka City. In 1994, the asparagus yield per ha was 2.6 t in open field but 3.9 t of asparagus was obtained by the mother stalk method in Hiroshima Prefecture. Furthermore, the yield reached 10 t from greenhouse cultivation in the Kyushu district, against an average 5.4 t for greenhouse cultivation in Japan as a whole.
