Blessing on lemons:
Lemons that are only mildly sour, and are thus edible, receive the blessing of Shehakol. Lemons that are very sour to the point of inedibility, do not receive a blessing at all prior to consumption.
Lemon peel: The peel of a lemon which is edible, receives the blessing of Shehakol prior to consumption.
 Ketzos Hashulchan 49:16; Brachos Guide in English Birchas Hanehnin; Brachos guide of Rav Prus; Seder Birchas Hanehnin 6:22 of Rav Elyashvili footnote 130
Other opinions: See Piskeiy Teshuvos 202:35 footnote 208 who states there are three types of lemons: a) Very sour and inedible-no blessing; b) Very sour but still edible-Shehakol. This is majority of lemons today; c) Mildly sour lemon-Haeitz according to Admur 205:1; d) Lemon juice with sugar is Haeitz if majority lemon juice; Vetzaruch Iyun Gadol on many of his points, as a) Admur 205:1 never states that a food that can be eaten “Beshas Hadechak” receives its set blessing; b) Admur explicitly states in many places [see below] that we follow the intent of the planting, if planted to eat in its current state; c) Where do these three types of lemons exist? d) How can one say Haeitz on a juice, in direct contradiction to the ruling in Michaber 202:23! Obviously, one may not rely on his words at all regarding this matter, and the ruling remains as stated above!
 The reason: As these fruits are edible in a time of need and thus they receive a blessing. [See Admur 202:4; Seder 6:1; Ketzos Hashulchan ibid and 49:7] However, their blessing is Shehakol, as all fruits that are not commonly planted to be eaten in their current state, but rather for use of seasoning, receive the blessing of Shehakol. [Seder Birchas Hanehnin 6:22; Luach 9:9; Admur 203:6 and 204:3-4 and 205:1; M”A 203:4]
 See Admur 202:4; Seder 6:1; Ketzos Hashulchan ibid and 49:7; Michaber 202:2; Birchas Habayis 1:49; Piskeiy Teshuvos 202 footnote 96
 See Admur 202:9; Seder 6:4 and 15; Ketzos Hashulchan 51:7 footnote 7