Gemara

89b (R. Yanai): Produce need be tithed only once it sees (is brought in through) the opening of the house - "I eradicated the Kodesh from the house."

(R. Yochanan): Even entering the yard obligates tithing it - "they will eat in your gates and be satiated."

Question (against both - Rav Chanina Chuza'ah - Beraisa): "K'Nafshecha" - a worker is like the owner. Just like the owner can eat without tithing, also a worker.

Inference: A buyer must tithe before eating!

Suggestion: This applies even in the field!

Answer (Rav Papa): No. The case is, a date tree is in a garden, and the foliage extends into a Chatzer (or according to R. Yanai, into a house).

The owner need not tithe before eating, for his primary concern is the tree itself. Since the tree is in the garden, the fruit is Kavu'a (must be tithed before eating it) only when all of it is brought inside. The buyer cares only about what he bought. Since that is in the Chatzer (or house), it is Kavu'a.

Question: Mid'Oraisa, one need not tithe bought Peros!

(Beraisa): The stores of Beis Hino were destroyed before Yerushalayim because they stuck to Torah law (and neglected a Rabbinical enactment).

"Aser... v'Ochalta" (tithe what you will eat), but not what you sell. "(Tithe) Tevu'as Zar'echa", but not what you buy.

Answer: A sale is Kove'a the Peros mid'Rabanan. Mid'Oraisa, it is exempt.

Question: (If so, also a worker is exempt.) What does "k'Nafshecha" teach?

Answer (Beraisa): "K'Nafshecha" - just like one who muzzles himself is exempt (from lashes), also one who muzzles a worker.

Question (Mar Zutra - Mishnah): The final processing for Ma'aser for gourds and pumpkins is from when Yifkesu.

(R. Asi): This is when the flower falls off the top.

Suggestion: This is even in the field!

Answer: No, it is in the house.

Question: If so (the Chidush is that it is exempt until then), it should not say 'from when Yifkesu', rather, 'not until Yifkesu'!

Answer: 'Until Yifkesu' connotes until all of them Yifkesu. 'From when Yifkesu' connotes from the beginning.

89b (Abaye): Dipping in salt is Kove'a for Ma'aser in Eretz Yisrael, but not in Chutz la'Aretz.

Objection (Rava): If it is Kove'a in Eretz Yisrael, it also is Kove'a in Chutz la'Aretz (where Chachamim enacted Ma'aser)! Rather, everywhere, salting one at a time (and eating it) is not Kove'a, but salting two (together) is Kove'a.

(Rav Masnah): We learn that salting two at a time is Kove'a for Ma'aser from "Ki Kibetzam ke'Amir Gorenah."

Beitzah 34b (Rav Nachman): Shabbos is Kove'a even unfinished produce.

35b (R. Yochanan): Shabbos, Terumah, Chatzer and a sale are Kove'a only finished produce.

Tana'im argue about all of these.

Rishonim

Rambam (Hilchos Ma'aser 3:3): Any one of the following six things are Kove'a for Ma'aser: the house, a sale, fire, salt, Terumah, and Shabbos.

Ra'avad: Why did the Rambam omit that pickling is Kove'a? The Mishnah (Ma'aseros 4:1) listed it separately from salt!

Ri Korkus: The Rambam explains that pickling is in saltwater, therefore he did not list it separately. This is like the Yerushalmi, which counted only six things. Even if it means in vinegar, like the Ra'avad holds, perhaps it is included in fire, for pickling is like cooking.

Rambam (ibid.): They are Kove'a only something that was finished.

Or Some'ach (5:2): The Rambam says that a sale of attached Peros is not Kove'a. The Yerushalmi infers that this opinion holds that a sale of detached Peros is Kove'a even unfinished Peros. The Rambam here says that it does not! It seems that a sale is not Kove'a until final processing. Then, the sale is Kove'a retroactively. The Rambam (3:6) says similarly about a house.

Rambam (4): If he sold Peros, cooked them through fire, pickled them with salt, separated Terumah, or Shabbos came, he may not eat until tithing, even though they did not reach the house. If he brought them into the house before final processing, he may eat Arai.

Rambam (ibid.): If he began final processing after they entered the house, he must tithe all of them.

Ri Korkus: The Rambam explains 'from when Yifkesu' connotes from the beginning, i.e. final processing on even one Pri obligates all of them. (Rashi explains that it is obligated once some flowers begin to fall off.)

Poskim

Shulchan Aruch (EH 331:83): Any one of the following six things are Kove'a for Ma'aser: the house, a sale, fire, salt, Terumah, and Shabbos. All of them are Kove'a only finished Peros.

Pischei Teshuvah (11): The Sha'ar ha'Melech (Ma'aser 5:22) says that also Yom Tov is Kove'a, for it is called Shabbos. Also, Shabbos is Kove'a because "v'Korasa l'Shabbos Oneg." The same applies to Yom Tov! However, the Me'iri says that Yom Tov is not Kove'a. The Pnei Yehoshua and Tzlach (Beitzah 40b and 35a) explain that there is no Mitzvah of Oneg on Yom Tov, only Simchah. Simchah is through Shelamim; Ma'aser does not apply to it.

Hagahos Sho'el u'Meshiv (on Tzlach Beitzah 35a): We rule that Oneg is obligatory on Yom Tov, like on Shabbos (OC 529:1). For Oneg Yom Tov, one may tithe even if the Peros being exempted and the Terumah are not together (Tosfos Gitin 31 DH ha'Meni'ach).

Note: The Pnei Yehoshua cited (without explaining) a proof from Beitzah 13a that Yom Tov is not Kove'a. The opinion that allows rolling Melilos (grain between one's fingers to remove the chaff) on Yom Tov holds that produce can become Tevel on Yom Tov. I.e. he entered grain to make a dough, and on Yom Tov decided to roll Melilos. If Yom Tov were Kove'a, all would agree that finished Peros brought inside on Yom Tov become Tevel on Yom Tov!

Tosfos Yom Tov (Ma'aseros 5:1 DH Lokach): The Rambam and Bartenura explain that a sale is not Kove'a attached Peros. In any case it is not Kove'a, because they are not finished! R. Shimshon says that a sale is Kove'a in a similar case of detached fruit, even though it is not finished. This is like the Stam Mishnah 2:5 (if people trade figs, they may not eat without tithing).

Shulchan Aruch (ibid.): Similarly, if he sold, cooked through fire, pickled with salt, separated Terumah, or Shabbos came, he may not eat until tithing, even though they did not reach the house.