Gathering the Heat of the Sun: World’s First Greenhouse

Today, the term “seasonal fruit (vegetable)” is becoming increasingly obsolete due to the availability of most fruits and vegetables year-round—a feat made possible by the greenhouse. This begs the question: did people who lived a long time ago eat only dried fruit and vegetables in the winter? Ancient Koreans were a hardy group: indeed, they built an ice storage facility in which ice stored in the middle of winter could be used in the hottest days of summer. It is interesting, to say the least, that the same Koreans are responsible for the world’s first greenhouse.

Article Lee Hyunju (Editorial Team) Sources “Joseon made the world’s first greenhouse!” (Hankyoreh), “World’s first eco-friendly ‘greenhouse of Joseon’” (Science Times)

ⒸKim Jeongheum

The first greenhouse was not built in Germany

Until recently, the world’s first greenhouse was thought to have been invented in 1619 in Heidelberg, Germany. It was a building that featured a simple, furnace-heated system. It turns out, however, that the first greenhouse was actually constructed in the Joseon dynasty 170 years earlier—and according to a much more sophisticated design—than its German counterpart.

A description of this greenhouse is found in Sangayorok (a book on agriculture and cooking; believed to be the oldest surviving Korean cookbook), which was written in 1450 by Jeon Sunui, a royal physician. The book, which contains information on diverse aspects of life for the commoner class, includes information on silkworm farming and how to restore crop damage as well as fruit trees, vegetables, and livestock and recipes for approximately 230 dishes. The explanation of the greenhouse is in the section on how to cultivate vegetables in the winter. The short (three line) description, in modern English, is roughly as follows:

The [greenhouse] can be built in any size, but three of the walls must be clay. The inner walls must be covered in paper, after which the paper is coated with oil. The south-facing wall must be latticed and covered in oil-coated paper. A gudeul may be installed on the floor, but it must be handled carefully so that smoke does not seep out. The gudeul must also be covered with a layer of soil [approx. 45cm thick]. In the evenings, wind must be kept from entering. On very cold days, windows must be covered with a thick straw mat that must be removed once the outdoor temperature rises. The indoor area must be sprayed with water daily so that the walls are covered in dew, and a mild temperature must be maintained to ensure that the soil does not dry up. The chimney must be installed separately from the building, with the place for the pot installed against the outer wall, so that on dry evenings, lighting the furnace makes the steam from the pot heat the entire indoor area.

This short but detailed explanation gives the impression that anyone, by reading it, could build their own greenhouse. The fact is, however, that the greenhouse was not invented by Jeon—which we know because there is an even earlier record of a greenhouse. Veritable Records of King Sejong mentions an experiment conducted in the 20th year of King Sejong (1428), by royal decree, to see whether tangerine trees could grow on Ganghwa Island. The explanation includes the following sentence: “the magistrate constructed a [greenhouse] in autumn and protected it from the elements by building a wall and installing an ondol.” There is also mention in Encyclopedia on Horticulture, which was written around the same time by Kang Hee-an, on a structure (tou (also, umjip)) whose functions are similar to those of a greenhouse. There is an incident in Veritable Records of King Seongjong described as follows: in 1471, the office responsible for cultivating the palace’s flowers presented the king with an azalea branch in the middle of winter. The king said, “Flowers that bloom in winter come from what is artificial” and requested that he not be given flowers that do not bloom in season. All of these mentions are instructive, but it is the description in Sangayorok that offers the most insight on how the greenhouses of Joseon worked. Even more incredible is the fact that this copy of Sangayorok was found in a pile of discarded paper in 2001: had it not been for this discovery, the greenhouse of Joseon would have still remained a secret today.

Source: Heritage of Korea (KBS)

Mulberry paper, the unsung hero of the Joseon greenhouse

The three most important aspects of a greenhouse are heat, humidification, and sunlight. Despite lacking modern technologies, the Joseon-era greenhouse worked just as effectively as its 21st-century counterparts. The first European greenhouse (and all modern greenhouses based on this design) raised the indoor temperature with furnace heat. This ends up heating only the greenhouse’s upper area: to cultivate crops, pots have to be used, or a separate cultivation facility installed on the ground. The Joseon greenhouse did not have this problem because the floor was equipped with a gudeuljang, which was covered with a layer of soil. This meant that vegetables and flowers could be planted in the soil (plants could also germinate and grow roots).

The ondol of the greenhouse was heated twice a day, morning and evening. Another daily task was boiling water in an iron pot over the agungi. The steam from the pot filled the indoor area, increasing both the temperature and humidity. In other words, there was no need to, as in Western greenhouses, constantly water plants to prevent them from drying up because of the dry, furnace-heated air. The Joseon greenhouse was perfect for cultivating plants because of the warm floor and air and regular humidifying.

Therefore, the factor that allowed the greenhouse of Joseon to be superior, in many ways, to its European counterpart is Korea’s traditional mulberry paper (hanji). In short, oiled mulberry paper substituted for the absence of sheet glass. The problem of greenhouses paneled with glass or vinyl is that dew forms on the inner walls whenever there is a significant indoor/outdoor temperature difference. Indoor dew has two adverse effects: it blocks sunlight, thus obstructing photosynthesis and lowering the indoor temperature, and also damages the leaves, petals, and fruit of the plants it falls on. A greenhouse coated in mulberry paper, however, has no dew. Korea’s mulberry paper is often called “breathable paper”: by coating it with oil, the paper was made waterproof. Moisture was, nevertheless, transferred through the minute gaps between the mulberry wood fibers. Mulberry paper was also conducive to bringing in more sunlight. Coating it in oil made the paper stretch taut and become thinner. This made it semi-transparent, which allowed more sunlight into all areas of the greenhouse.

Sophistication of Joseon’s technology continues to fascinate in the 21st century

Unfortunately, despite the sophistication of the Joseon greenhouse, there are no surviving records of it after the 15th century. Experts believe that the lack of its widespread use was due to the inability of commoners to build a greenhouse, without royal funds, and prepare firewood and oiled mulberry paper for it.

The academic community has created several replicas of the Joseon greenhouse based on the Sangayorok description. The first one was made by Professor Kim Yongwon (Keimyung College University) in 2002 in Namyangju, Gyeonggi-do. After planting radishes, lettuce, cabbages, wild chives, spinach, and beets, Kim measured the greenhouse’s temperature and humidity. His measurements showed that the temperature of the space just above the ondol was consistently warm (at least 20 degrees Celsius), while the overall indoor temperature was always at least 10 degrees Celsius. The indoor humidity increased, after the influx of steam from the pot’s boiling water, making it noticeably more humid than the space outside the greenhouse. The vegetables, of course, grew without any problems. Kim’s replica proved that the greenhouse of Joseon was as advanced as records suggest.

The earliest Western greenhouses used animal feces to raise the indoor temperature. The feces, albeit eco-friendly, emitted such a strong stench that an alternative method had to be found. The alternative, coal, produced toxic gases when burned. Had pains been taken in a timely manner to spread the technologies and materials (ondol, mulberry paper) involved in the traditional Korean greenhouse, which is devoid of pollutants and dew—the biggest drawback of the modern greenhouse—the greenhouse of Joseon may have enjoyed a global following. There is seemingly no end to the surprising wisdom of ancient Koreans.