Shade cultivation of tea (Japanese: 覆下栽培, romanized: ōishita saibai), also called covered cultivation, is a Japanese method of tea cultivation in which tea bushes are covered before harvest to reduce their exposure to sunlight. The plants are generally shaded for approximately one to four weeks, depending on the type of tea and the intended quality. The two principal methods are overhead canopy shading, in which covering materials are suspended above the plants, and direct covering, in which shading fabric is laid on the surface of the tea bushes. Shading alters the growth and chemical composition of the new shoots. It suppresses the decrease in free amino acids and the accumulation of catechins that normally occur as the shoots develop, producing tea with stronger umami and less astringency. It also increases the leaves' chlorophyll content, giving them a deeper green colour, and produces a characteristic aroma known as 覆い香 (ōika, "covering aroma"). The technique is used primarily to produce leaves for gyokuro, kabusecha, and tencha, the raw material from which matcha is made. Shade cultivation developed in the Uji tea-producing region. The Jesuit missionary João Rodrigues described covered tea gardens in late-16th-century Uji in his 17th-century História da Igreja do Japão. A 2019 soil study of the Okunoyama tea garden in Uji concluded that shade cultivation at that garden had probably begun by the first half of the 15th century.
History
Origins Before the publication of the 2019 soil study, the origins of shade cultivation had generally been inferred from historical records describing covered tea gardens in the second half of the 16th century, although the precise date at which the practice began remained uncertain. One of the principal written accounts is the História da Igreja do Japão by the Jesuit missionary João Rodrigues. Rodrigues described tea gardens in Uji where frames were erected over the plants and enclosed with mats made from reeds or straw. According to his account, the coverings were used to protect the soft and delicate new shoots from frost damage. In 2019, researchers examined the soil profile of the Okunoyama tea garden in Uji. They analysed soil carbon content, rice-derived phytoliths, and radiocarbon dates. An increase in rice-derived phytoliths and carbon in a soil layer dated to between 1396 and 1440 was interpreted by the researchers as evidence that large quantities of rice straw had been applied to the garden. They therefore estimated that shade cultivation at Okunoyama had begun by the first half of the 15th century, approximately 150 years earlier than had previously been inferred from historical documents. Covering appears initially to have been intended principally to protect new shoots from frost. Growers subsequently recognised that leaves grown under cover differed from open-grown leaves in colour, flavour, and aroma. The practice consequently developed from a protective measure into a means of controlling and improving tea quality. The development of shade cultivation contributed to the characteristic deep-green colour, umami taste, and aroma of later Japanese tencha and matcha.
Spread from Uji
From the late medieval period into the Edo period, the use of shade cultivation was restricted to certain authorised tea producers in Uji. Their economic position later deteriorated under measures including tea-price controls imposed by the Tokugawa shogunate. A major fire in Uji in 1698 destroyed covered tea gardens, tea-processing facilities, and residences. Because it became difficult to maintain the supply of tencha, tea producers in surrounding districts were subsequently permitted to employ shade cultivation. The technique therefore spread beyond Uji, while the exclusive position of the Uji tea masters weakened. In 1738, the tea grower Nagatani Sōen is traditionally credited with developing the aosei sencha seihō, the steaming and hand-rolling method that became the basis of modern sencha manufacture. In the 1830s, gyokuro is said to have emerged through the application of sencha-style processing to leaves grown in covered gardens. During its early development, leaves from the same covered garden could be processed either as tencha or as gyokuro. The mechanisation of tea processing in the early 20th century contributed to increasing specialisation of tea gardens and factories by tea type. From the mid-1980s, matcha began to be used more widely as a food ingredient. During the following decades, demand for matcha used in ice cream, confectionery, beverages, and other processed foods increased. Production of comparatively inexpensive processing-grade tencha and kabusecha consequently expanded, and direct covering became the principal shading method used for this sector because of its lower cost. By the 2025 crop year, Japanese tencha production was approximately 3.2 times its 2014 level.
Methods The covering material, shading rate, date on which covering begins, and duration of covering vary according to the intended tea type, cultivar, harvest season, local climate, and desired quality. Traditional gyokuro and high-grade tencha are generally shaded with material having a high shading rate for approximately 20 to 30 days. Kabusecha is commonly shaded for approximately 7 to 15 days, while brief covering of about one week may be used principally to improve leaf colour.
Covering materials The traditional covering materials are reed screens called 葭簀 (yoshizu) and rice straw. A method using these natural materials is known as 本ず (honzu) covering or honzu cultivation. A traditional rule is expressed as "ten days under reed screens and ten days under straw". The garden is first shaded for approximately ten days with reed screens. Straw is then spread over the screens for a further ten days, raising the final shading rate to approximately 98 per cent. Woven straw or rush mats may also be used. Traditional honzu cultivation has declined because suitable reeds and straw are difficult to obtain and because spreading the straw evenly over the canopy requires skilled labour. Since the late 1970s and early 1980s, black synthetic materials containing carbon have become widely used. Modern covering materials are commonly made from polyethylene or polypropylene shade netting; Vinylon was also formerly used.
… excerpt ends here. Continue reading the full article.
