On August 15, 1945,
Korea won its independence; Dr. Woo resigned from his positions at the Takiyi research farm and Tokyo University, and prepared his own place near a Buddhist temple. In Korea, farmers were left no seeds to plant because trade between Korea and Japan ceased, and the seeds were produced only in Japan. The policy was aimed to hinder Koreans from obtaining technological knowledge and to profit from selling the seeds to Koreans at a high price. As a result, after the liberation, there were neither people nor companies in Korea which could produce vegetable seeds such as
radish and
Napa cabbage, and seeds could not be imported from Japan. In accordance to a suggestion by Kim Jong-yi to resolve this problem,
President Yi Seung-man sponsored a campaign to urge for Dr. Woo's return; Dr. Woo complied, and a team was established to allow Dr. Woo to work as soon as he returned to Korea. The team worked to gather money and resources, and established the "Hanguk Nong'eop Gwahak Yeonguso" () or Korean Agricultural Science Research Institute near the city of
Busan. Unfortunately, as a Japanese citizen, Dr. Woo was not allowed to leave Japan for Korea. He therefore collected his papers which had traced his ancestral lineage from Korea, and went to a Japanese office which searched for illegal Korean inhabitants. The employees were shocked that a world-renowned scientist would voluntarily bring himself to the office. In March 1950, Dr. Woo returned to Korea. The team that was assigned to prepare for Dr. Woo's return welcomed him, holding a sign that read "Welcome! Dr. Woo Jang-choon's return home." A few days later, a welcome ceremony was held in Dongrae Won'e High School, and Dr. Woo delivered a speech: "Unfortunately, I worked for my mother's country, Japan, for fifty years. During those years, I worked for Japan no less than any other Japanese. From now on, I will work for my father's country, my home country, with all of my effort. And I will bury my bones in my home country." After a trip around the country, Dr. Woo observed the poor conditions of the farms, and concluded that mass production of seeds was imperative. In addition to these desperate circumstances, the
Korean War began only three months after Dr. Woo's arrival in Korea. Luckily, the
Busan area was able to avoid conflicts, and Dr. Woo could work uninterrupted. Because there were not many
insecticides available, Woo concentrated on producing seeds that were less susceptible to bugs. He did not neglect planting flowers, which seemed to not be a concern for a country in destitute conditions. The research institute became filled with countless beautiful flowers, and many visitors came by to enjoy the scenery. Once, an
American
colonel made a visit to the institute, and saw a double-flower
petunia. He quizzed an employee about the inventor of the flower. When the employee pretended to be ignorant on the subject, the colonel said that it was a Japanese scientist named Dr. Woo. To his surprise, Dr. Woo was a Korean working at the same institute, and the colonel returned with gifts to meet Dr. Woo. For a country not self-sufficient in producing crops to sustain and feed the country's population, the most crucial requirement was the development of top quality seeds to improve crop production. Woo Jang-choon's work resulted in improved seeds for many of Korea's staple crops, starting with
Korean cabbage, the
icicle radish, hot peppers, cucumbers, head cabbage, onions, tomatoes,
watermelon, the yellow
chamui melon. Other major horticultural breakthroughs from Woo's research included germ-resistant seed potatoes, the
seedless watermelon, and the Jeju variety of
tangerine (). Later, the Korean Agricultural Science Research Institute was renamed Central Agricultural Technology Research Institute (). Dr. Woo received a letter from his wife, Koharu, about his mother's poor health; he, therefore, requested the president to allow him to visit
Japan, but this was not allowed. Eventually, Dr. Woo's mother died, and Dr. Woo mourned that he could not repay his mother for all she had done. This made it into the news, and there was a nationwide effort of sending letters and donations to Dr. Woo. As a memorial to his mother and to meet the needs of his employees, Dr. Woo dug a
water well near his laboratory, and named it "Jayucheon" (자유천, short for 자애로운 어머니의 젖 같은 샘) or "The Well that is like the Milk of a Loving Mother". Many agricultural decisions during the 1950s were made according to Dr. Woo's suggestions, or made by Dr. Woo himself. This included the planting of
cosmos flowers to decorate the highways and railroads. Cosmos flowers disseminate easily, and would not be targeted by farmers to feed the livestock because they are toxic in nature. One exception was on the topic of introducing
hydroponics, in which Dr. Woo suggested sanitary culture, instead, because it was a much cheaper alternative with the same result; although a
hydroponics facility was installed in
Suwon, the outcome was poor. The president suggested sending researchers to Japan to learn the secrets of hydroponics, but Dr. Woo said that hydroponics does not require special techniques other than clean water, the right balance of the nutrients, and time. Dr. Woo's team established a sanitary-culture facility in
Seoul (the capital city of Korea), and its success was signified when the
US military noted the facility's hygienic products and chose the facility to supply its soldier
fruits and
vegetables. Dr. Woo also succeeded in producing germ-resilient
seed potatoes. ==Illness and death==