Sheviis, Chapter 2, Mishnah 6. This mishnah deals with the question of which activities may be performed on a tree in the year before Sheviis, and how much time must be left before Rosh Hashanah.
The text of the mishnah:
"Ein notin ve'ein mavrichin ve'ein markivin erev sheviis pachos mishloshim yom lifnei Rosh Hashanah" - three activities are forbidden here, and for all of them a margin of thirty days before Rosh Hashanah is required:
Netiah (planting) - planting a tree.
Havrachah (layering) - taking a branch of a tree or of a vine and placing it in the ground in such a way that it emerges and sprouts up in another spot.
Harkavah (grafting) - grafting one tree onto another.
"Ve'im nata o hivrich o hirkiv - ya'akor" - one who transgressed and performed one of these activities within the thirty days is obligated to uproot it and undo what he did.
The time periods - three opinions:
The first Tanna: thirty days before Rosh Hashanah.
Rabbi Yehudah: "Kol harkavah she'einah koletes lishloshah yamim - einah koletes" - any graft that does not take hold within three days will not take hold at all. Although he speaks of grafting, he does not mean grafting alone but every one of the plantings mentioned: if the planting has not taken hold within three days, it will no longer take hold and will not take root. Therefore three days alone suffice, and not thirty.
Rabbi Yosi and Rabbi Shimon: "Lishtei shabbasos" - two weeks, fourteen days. As long as the activity was performed fourteen days before Rosh Hashanah, it is permitted.
The approach of the Gemara in Rosh Hashanah:
Some understand that the Gemara in Tractate Rosh Hashanah bears on our mishnah, and according to it all of these time periods - the thirty days of the first Tanna, the three days of Rabbi Yehudah and the two weeks of Rabbi Yosi and Rabbi Shimon - were stated in addition to the thirty day addition to Sheviis. According to this understanding:
According to the first Tanna - sixty days before Rosh Hashanah.
According to Rabbi Yehudah - thirty three days.
According to Rabbi Yosi and Rabbi Shimon - forty four days (fourteen plus thirty).
However, not everyone agrees that that Gemara is relevant to our mishnah, and some explain the mishnah at face value: according to the first Tanna - thirty days before Rosh Hashanah, according to Rabbi Yehudah - three days before Rosh Hashanah, and according to Rabbi Yosi and Rabbi Shimon - fourteen days before Rosh Hashanah.
In summary: in this mishnah we learned the prohibition against planting, layering and grafting in the year before Sheviis within thirty days of Rosh Hashanah, and the obligation to uproot whatever was done in violation of it. We examined the three opinions as to the required time period - thirty days, three days or two weeks - and the two ways of understanding them: whether these periods are added to the thirty day addition to Sheviis, or whether they are counted at face value from Rosh Hashanah.