During the Muromachi period, a newly developed drying technique allowed kombu to be stored for more than a few days, and it became an important export from the Tohoku area. By the Edo period, as Hokkaidō was colonized and shipment routes were organized, the use of "kombu" became widespread throughout Japan. Traditional Okinawan cuisine relies heavily on "kombu" as a part of the diet; this practice began in the Edo period. Okinawa uses more "kombu" per household than any other prefecture. In the 20th century, a way to cultivate kombu was discovered and it became cheap and readily available.