What is Covered Cultivation?

Written by Misato T

Covered cultivation is a farming method in which tea gardens are shaded with black sheets, such as those made of woven fabric called kanreisha or straw. This method is unique to Japanese tea farming and is used to produce teas with rich umami flavor, such as matcha, gyokuro, and certain types of sencha (kabusecha).

When Did Covered Cultivation Begin?
Covered cultivation (or shaded cultivation) began over 400 years ago in Kyoto. Originally, the purpose of covering was to protect the young tea buds, which sprouted in early spring, from damage caused by late frosts. However, it became evident that the presence or absence of covering significantly affected the quality of the tea. High-quality tea was often produced in tea gardens surrounded by forests with frequent mists and relatively low sunlight. Over time, covered cultivation evolved into a technique for producing high-quality tea.

In the past, straw and reed screens (yoshizu) were used for shading. This cultivation method was originally exclusive to tea gardens in Uji, which were granted the privilege of producing matcha. This exclusivity is one of the reasons Uji became famous for matcha production. Although some tea gardens still use straw and reed screens for covered cultivation, it is now more common to use sheets called kanreisha, which are easier to manage.

Traditional Covering Method Using Straw

Reasons for Covered Cultivation

Reason 1: To Produce Tea with Strong Umami
Covered cultivation is widely practiced in Japan to create tea with a rich umami flavor. While tea cultures in other countries often emphasize "aroma," Japanese tea places greater importance on taste, particularly umami, though aroma is also considered to some extent.

Theanine, which accounts for over 40% of the umami components in tea, is synthesized in the roots of the tea plant and accumulates in the leaves. However, exposure to sunlight converts theanine into catechins, which contribute to astringency. By shading the plants, this conversion is suppressed, resulting in tea with stronger umami and reduced astringency.

Reason 2: To Deepen the Green Color of the Leaves
Shading the tea plants creates a low-light environment, forcing the plants to perform photosynthesis with limited light. To adapt, the leaves become thinner and broader while increasing chlorophyll production to enhance photosynthesis efficiency. This process results in a deeper green color in the leaves.

Reason 3: Frost Protection
During the spring, when the first flush (ichibancha) is harvested, frost can sometimes form in the early morning. Covering the tea garden provides some degree of frost protection, reducing potential damage to the leaves.

Reason 4: Preventing Leaf Hardening
As tea leaves grow, their carbon content increases, causing the leaves to harden and their quality to deteriorate. By shading the tea plants, their growth slows down, delaying leaf hardening and allowing for a later harvest period without compromising quality.

Timing of Shading
In covered cultivation, shading begins when 2–3 new leaves have emerged and continues until just before harvest. If shading starts too late, the number of new buds and their growth may be insufficient, leading to extremely low yields. The timing of shading is critical and is decided based on factors such as weather, labor availability, and the condition of the tea leaves.

Two Methods of Shading: Tana-gake and Jikakake
There are two primary methods of shading in covered cultivation:

1. Tana-gake (Framework Shading)
   In this method, tea leaves are shaded under a structure resembling a tent. Tana-gake prevents direct contact between the shading material and the leaves, allowing the tea plants to grow freely without damage. Additionally, it prevents heat from building up under the cover, resulting in higher-quality tea. However, constructing such structures can be costly and challenging, especially in areas with unsuitable terrain.
   

2. Jikakake (Direct Shading)
   In this method, the shading sheets, such as kanreisha, are directly placed over the tea garden. While this approach is more versatile and can be implemented in various locations, it may result in some damage to the leaves and lower quality compared to tana-gake.