A brief history of the Ordan Esrog
The “Ordan” strain of esrog had humble beginnings but is now the most popular esrog worldwide.
Around the year 1850, Sir Moses Montefiore was instrumental in establishing esrog plantations in Eretz Yisroel, in order to help the Jewish settlers to survive. The early Sephardic settlers had a long held tradition regarding the beauty and kashrus of the Corfu variety esrog (from Greece), and therefore Montefiore chose to transplant its seeds under the guidance of the local Sephardic Rabbi Yehuda Halevi to the city of Yaffo.
Rabbi Avraham Yitzchak Kook founded and headed the "Atzei Hadar" union for kosher esrog cultivators and marketers, and promoted the intraspecific grafting of the Yaffo grown Corfu esrogim with Balady esrogim (which is permitted by Halacha). This led to the establishment of a beautiful variety of kosher esrogim, grown in Eretz Yisroel with the holiness of the land, and which saved the economy of Israel for decades. However, whilst this was a great idea from a practical and Halachic perspective, it induced suspicion from some authorities who wondered how these esrogim could be so beautiful without grafting.
A shochet from Chadera by the name Ordang had a tree of these esrogim growing in his backyard. The tree was tested and assessed by many Gedolei HaDor to have a chezkas kashrus as being ungrafted.
Today, most Chasidic communities in Eretz Yisroel, as well as in the diaspora, use descendants of the “Ordang” or “Ordan” strain (and tree) which were planted under the highest Rabbinical Hashgachos.