Peeling produce:[1]

Many have the custom to peel all their fruits and vegetables and to avoid eating anything which cannot be peeled. [For this reason, some do not eat lettuce past the night of the Seder. Others are not particular in this.]

Use separate knife for peeling the fruits/veggies: Many have the custom to designate a separate knife or peeler for the peeling of all the fruits and vegetables throughout Pesach. The knife is not used to cut through the fruit/vegetable.

Peeling on Yom Tov using a peeler?[2] It is permitted to use a peeler on Yom Tov to peel all fruits and vegetables.

Peeling on Shabbos using a peeler?[3] Those fruits and vegetable which majority of people do not eat together with the peel, and it is rather removed and discarded prior to eating, according to all opinions, it is [Biblically[4]] forbidden to use a peeler to remove the peel on Shabbos.[5] This applies even if one intends to do so in order to eat the food right away. Those fruits and vegetables which majority of people eat together with the peel, some Poskim[6] rule it is forbidden to be peeled using a peeler, and rather may only be peeled with a knife for right away use.[7] Other Poskim[8] however rule it may be peeled using a peeler, and may even be peeled for later use on Shabbos.[9] Practically, those who are stringent are doing a proper act, although those who are lenient have upon whom to rely, and each person is to ask his Rav.[10] Those who are particular to not eat peels on Pesach, and hence peel all their produce, seemingly may still abide by the leniency of using the peeler on Shabbos Pesach for peels that are generally eaten by majority of people, if they are accustomed to follow the lenient opinion during the other Shabbosim of the year.[11]

May I cook vegetables and fruits with peels in my Pesach pots before Pesach?[12] One who chooses to be lenient may do so even if in general he peels all of his produce on Pesach. However, those who desire to be stringent in all the Pesach stringencies, should avoid doing so even before Pesach, and so is the attested custom of some esteemed Chabad families.

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[1] Chayeh Adam 127:2; Nitei Gavriel 2 39:14 ; This stringency is not mentioned Otzer Minhagei Chabad, although it is a widespread custom amongst Chabad to do so; See Teshuvos Vehahagos 225 that one needs to peel his fruits and vegetables before eating them as there is suspicion that they were sprayed with a Chametz containing ingredient.

[2] Piskiey Teshuvos 504:3; Nitei Gavriel 5:14 based on Admur 510:6

[3] See Rama 321:19, Admur 319:9, M”B 319:22 and 24 that peeling is subject to the Borer prohibition: Shabbos Kehalacha Vol. 2 p. 294 and 299-307; Piskeiy Teshuvos 321:34-35

[4] The reason: As a peeler is the normal vessel used to remove the peel from a fruit/vegetable and hence is similar to a sieve and sifter, which is Biblically forbidden to be used. [See Admur 319:1; M”B 319:2; Rashi Shabbos 74a]

[5] Iglei Tal Borer 6; Ketzos Hashulchan 125:16; Piskeiy Teshuvos 321:35

The reason: As a peeler is a designated item for separating and negates the required condition of separating with one’s hands. [ibid]

[6] M”A 321:19 regarding apples; Elya Raba 321:30; Tosefes Shabbos 321:41; M”B 321:84; Orchos Chaim 319:22 in name of Meorei Or; Igros Moshe 4:74 Borer 8; Az Nidbaru 9:10; Chut Shani 25:7

[7] The reason: As these Poskim hold that the separating prohibition applies to even edible peels and thus when peeling it one must abide by all Borer restrictions, which include not peeling it with a peeler, and even when using a knife, to only do it for right away use. The reason that even edible peels contain the Borer restriction is because when they are peeled off, they are generally thrown out, and hence have a status of Pesoles when one comes to peel it. [Piskeiy Teshuvos 321:34]

^[8] Peri Megadim 321 A”A 30, brought in Shaar Hatziyon 321:97; Iglei Tal Borer 6:12; Shevisas Hashabbos Borer 24 and footnote 45; Kaf Hachaim 321:141; Ketzos Hashulchan 125:16 [see however Ketzos Hashulchan 126 footnote 19]; SSH”K 3:34

[9] The reason: As according to these Poskim, edible peels do not contain a Borer prohibition, and hence there is no need to abide by the Borer conditions which restricts one from using a Borer instrument and requires the peeling to be done for right away use. Regarding if the peeler contains an Issur of Muktzah or Uvdin Dechol-see Piskeiy Teshuvos 321:35 footnote 373-374

[10] Minchas Shabbos 80:69 that it is proper to be stringent when possible, and so concludes: Shabbos Kehalacha ibid; Piskeiy Teshuvos 321:34-35 that it is best to be stringent when possible, although one who is lenient has upon whom to rely; Michzei Eliyahu 1:51-52; Teshuvos Vehanhagos 1:208

Ruling of Rav Farkash in Shabbos Kehalacha ibid: Rav Farkash rules that one who wishes to be stringent like all opinions [which he rules one initially is to do], is to always apply the separating restrictions to anything being peeled. In a case that one is pressured to peel using a peeler, such as when one has a lot of fruits/vegetables to peel, or in a case that one is pressured to peel the fruits a while prior to the meal, such as in a case that one must leave one’s house now and will only return when the meal will commence, then although one may be lenient like the latter opinions, nevertheless it is proper to also cut off part of the actual fruit together with the peel. [Shabbos Kehalacha 13:9; Piskeiy Teshuvos 321:34]

[11] The reason: As the peel itself is still viewed as a food, and it is simply due to its Chametz contingency that people avoid it, and not because they suddenly view the actual peel as Chametz or inedible. Accordingly, at the very most they are removing the bad [Chametz] with the good [the peel] of which many Poskim rule is permitted, and hence the leniency would still apply according to the lenient opinion.

[12] Explanation: Strictly speaking, from the letter of the law, there is no requirement at all to peel the produce which one eats on Pesach, and a simple washing suffices. The stringency of peeling produce is not recorded in the  Poskim, and is a mere hand down tradition among some communities. Accordingly, certainly from the letter of the law one may cook produce that is not peeled in his Pesach pots. Now, with regards to those who are generally stringent on Pesach to peel their produce, an argument can be made to be lenient being that before the night of Pesach the prohibition of Mashehu by Chametz does not apply, and it is hence nullified in 60 times. [Admur 447:1] On the other hand, an argument can be made to be stringent even before Pesach to peel all produce that will be cooked in the Pesach pots being that some opinions hold that Chametz is Chozer Veniur on Pesach [See Admur 447:22], and indeed Rav Landau of Bnei Braq has stated that the custom is to peel all produce, even before Pesach, when cooking in Pesach pots. [See Hearos Ubiurim 1086 p. 126]