In Japan, nearly 80 percent of mat rush is grown in Kumamoto prefecture, Kyushu. Of this, rush grown in Yatsushiro is famous for its high quality.
In rush cultivation, seedlings are raised from late August to sometime in September, and these seedlings are planted in fields from late November through December. The planting season varies depending on the cultivar, and there are three varieties: “early harvest,” “ordinary harvest,” and “late harvest.”
Before being processed, harvested rush undergoes “dorozome” (mud dyeing) by being soaked in natural mud. Mud dyeing accentuated the good fragrance unique to the rush and increases strength. After that, it is dried in a dryer until its moisture content becomes 10% or less. In this way, the rush is finished before being finally processed into tatami.