Yoshizu - Traditional Methods of Tea Shading

Last month, Daiki-san, Hiroki-san, and I headed to the shores of Lake Biwa. Japan’s largest lake, to learn more about Yoshizu. Yoshizu are traditional woven screens made from reeds, or yoshi, which are used for shading high-grade teas like tencha and gyokuro. In Japanese tea cultivation, shading is a critical process where tea bushes are covered for multiple weeks before harvest to block out direct sunlight. This stress forces the plants to produce more chlorophyll and L-theanine, resulting in that vibrant green color and the deep, savory umami flavor that defines high-quality matcha. When reeds are woven together, they create a living canopy for tea trees. Unlike synthetic covers that are most often used in the tea world, this natural barrier allows for a subtle exchange of air and diffused light, resulting in incredibly high quality, deep umami matcha.

Harvesting & Selecting the Reeds 

When we arrived at the Biwa wetlands, the first thing that hits you was the scale of the reeds and of the area they take up: they’re massive. To harvest them, a specialized cutting tractor is used that severs the reeds at their base, but it cannot do the job alone. Workers stand right behind it, working in sync with the machine to grab the fallen stalks as soon as they are cut. It really drives home how much physical labor still goes into "traditional" tea production before the tea is even planted.

Once the reeds are down, the next part of the work starts: the selection. We sat with Sanada-san, who is one of the heads of this reed crafts company. She has been a craftswoman for 15 years, and she taught us how to "read" the reeds. The goal of the selection process is to separate the yoshi (“good” reeds) from the ashi (“bad” reeds). Yoshi are resilient, thick, and straight, while ashi have higher water content, are thinner, and overall not as good for construction. Helping with the sorting, you realize how much is discarded to ensure only the best material makes it to the next step. 

Depending on the season and the year, the water levels around Lake Biwa can also heavily fluctuate. Ashi and Yoshi prefer different levels of water, and as such the overall distribution of good and bad reeds can change year to year, which affects the ease of the selection process.

A Part of the Ecosystem

After the reeds are selected and dried, they are woven into screens. They are not only used for tea shading, however! There are many traditional applications for these yoshi, from Japanese sudare screens, to one I find most impressive, thatched shrine roofs (kayabuki)! We had the chance to see the construction of a temple roof using the reeds, which was incredibly interesting. These reed roofs usually last around 30 years, and are symbolic of these temples’ harmony with nature.

Because Lake Biwa is a protected landscape, reed harvesting isn't just a business; it’s a vital environmental cycle. As the reeds grow, they filter the water and purify the air, acting as the 'lungs' of the region. The harvest isn't just about taking from the land, it’s a necessary thinning that allows the ecosystem to breathe and regenerate for the year ahead. In this way, the craftswomen and men are the caretakers of the lake. It is a natural dialogue between the land and the people who protect it.

This trip to Lake Biwa was incredibly fun, and a powerful reminder that the matcha we drink is part of a much bigger ecological loop, and the result of so many people’s work.

For those interested for a more visual recounting of our time at Lake Biwa, check out this Youtube video.