When do Lemons become Kedushas Shevi’is?
Lemons have the same Halachic status as an Esrog regarding Shemita. [Thus, if they are picked after Rosh Hashanah of the Shemita year, they are to be treated with Kedushas Shevi’is due to Safek, but are to also have Terumos and Maasros removed from them without a blessing until they are for certain to be considered Kedushas Shevi’is, as explained next. However, some are lenient to treat lemons as any other fruit, in which case we follow the time of the blossom regarding Kedushas Shevi’is. According to this opinion, lemons will begin their status of Kedushas Shevi’is on the 1st of Iyar, and end it the next year on the 14th of Iyar, and according to all opinions it is to be treated as definite Kedushas Shevi’is starting from this date.]
The law by an Esrog: It is disputed if we follow the blossom of the Esrog [i.e. like fruits] or the picking of the Esrog [i.e. like vegetables] regarding the Shemita laws. It is likewise disputed whether we follow the beginning of the 7th year, or the 15th of Shevat of the 7th year. Practically one is to be stringent like both opinions and remove from Esrogim that blossomed in the 6th year but were picked in the 7th year, Terumah and Maaser without a blessing and the fruit is to be treated as Kedushas Shevi’is. Practically, for the Sukkos of the Shemita year one is to be stringent to purchase an Esrog that was picked prior to Shemita, and hence satisfy all opinions. In the Sukkos of the eighth year however the Esrog is treated as Kedushas Shevi’is and hence may only be purchased through Otzer Beis Din.
 Rav Shlomo Sirila [i.e. Rasha”s] Shevi’is 9:4 [p. 136]; Grach Naah p. 11 “The lemon has the same law as the Esrog”; Chazon Ish 9:17; Directive of Rav Mordechai Eliyahu; See Derech Emuna p. 240; Kerem Tziyon p.80; Menachem Yerushalayim 104; Sheves Ha’aretz Kuntrus Achron 18; Shemita Kehilchasa p. 27; Yalkut Yosef Shemita p. 555
 Chazon Ish 21:16; Rav SZ”A in Minchas Shlomo 1:51-22; See Kedushas Hashevi’is 17:14; 38:6
 See Rosh Hashana 14b; Rambam 4:12
 Perhaps it is treated like a vegetable being that it grows daily from its water, similar to a vegetable and we should hence follow the day of its picking, being that on that day it also grew from the water. [Grach Naah p. 11; See Rashi R”H 12b] Other Poskim however rule that we follow the blossom of the Esrog just like any fruit tree. [Raavad Maaser Sheiyni 1:5; Rashi Rosh Hashanah 15b; Tosafus R”H 15a; Gr”a Y.D. 331:191]
 Rambam ibid; Grach Naah