Summer Lettuce Melting in the Heat Wave, Can a ‘Disaster-Resilient Variety’ Be the Answer?

As severe climate change, heat waves, and hot, humid weather continue, concerns are deepening among greenhouse vegetable growers in midsummer. In summer lettuce cultivation in particular, even existing popular varieties are showing reduced marketability due to various physiological disorders such as tip-burn, in which leaf edges scorch, and soft rot, in which leaves melt down.

In fact, according to a lettuce monograph published by the Rural Development Administration in 2017, leaf lettuce has problems such as bolting during high temperatures, unstable red coloration, and high harvesting labor requirements, while head lettuce suffers frequent bolting and rot diseases (sclerotinia and soft rot) when grown in hot periods, making cultivation particularly difficult during the summer high-temperature season from July to September.

‘A paper titled ‘Effects of Foliar Calcium Application on Growth and Leaf Calcium Content in Lettuce Cultivated During High-Temperature Periods’ also states that the optimal growth temperature for lettuce is 15–20℃, and the suitable temperature for heading is 10–16℃. It noted that lettuce has relatively strong tolerance to high temperatures in the early growth stage, but this weakens as growth progresses, and at 24–26℃ or higher, growth is suppressed and diseases occur frequently.

Amid these cultivation characteristics of lettuce, which make summer heat a challenge for farmers, ‘Jincheongmat,’ a green skirt lettuce variety, is drawing attention as a disaster-resilient variety.

Lettuce growers in summer often struggle because lettuce becomes limp just before harvest or during post-harvest distribution. However, ‘Jincheongmat’ is a variety developed to maximize excellent shelf life and marketability so that it does not soften easily even in the hot and humid summer environment. Its dense tissue helps it maintain lettuce’s characteristic shape and firmness even in the heat, offering the advantage of preserving freshness for a long time even during packaging and long-distance transport after harvest.

Lettuce grown in hot weather usually tends to become tougher in texture or more bitter in taste, but ‘Jincheongmat’ retains its distinctive crisp taste even in midsummer, winning over consumers. The leaves also grow uniformly to the most suitable size for wraps without becoming overly elongated or disordered, making it advantageous for receiving high grades in wholesale market auctions and for supplying fixed buyers such as large supermarkets and restaurants that demand high quality.

In addition, because its yield is high for the same area, it is regarded as a star variety that can maximize farm profits during midsummer, when lettuce prices soar and lettuce becomes as valuable as gold. Jincheongmat can be produced almost year-round, and from transplanting to harvest it takes about 25 days in summer and about six weeks in winter. It is also highly tolerant of humidity, making it strong during the rainy season.

Heo Young-suk, vice president of the Jeonbuk Lettuce Research Association, said, “Jincheongmat has a longer storage period than other lettuces, and for the same area during the same period, production is 20–30% higher,” adding, “Although there is a difference between summer and winter harvest volumes in a year, based on 250 pyeong, it is harvested about 48 times annually, and on average 70 boxes of 4 kg each are harvested per harvest, bringing annual production to over 10 tons.”

According to KAMIS, the agricultural and fishery product price information system of the Korea Agro-Fisheries & Food Trade Corporation, the average annual auction price for 4 kg of lettuce in 2025 is 24,866 won (6,221 won per kg). If a farm producing 7–8 tons annually increases output by 20–30%, that would mean an improvement in annual farm sales of about 10 million won.

Vice President Heo explained, “Jincheongmat sometimes shows tip-burn during dry spring conditions, but because it is humidity-tolerant, there is almost no tip-burn during the humid summer.” She also added, “Because it is crisp in texture and does not soften, it is being widely used in salads and sandwiches as an alternative to iceberg lettuce, which is difficult to supply in summer, and recently the consumer base has grown significantly.”

Kim Su-ho, secretary-general of the Jeonbuk Lettuce Research Association, explained, “There is also an explanation that Jincheongmat bolts late, but this varies depending on the environment, so it cannot really be called an advantage of Jincheongmat,” adding, “Tip-burn can also appear differently depending on management.”