Each year has four days, which are its "beginnings". It is the 1st Nisana, the 1st Elula, the 1st Tyshrea and the 15th sewing-that bi-sew (that bi-sew on Hebrew literally-15th seamstress; the numerical meaning of the Jewish letters - fifteen).
The 1st Nissan is the beginning of the year in terms of calculating the reign of the kings of Israel, as well as the order of the holidays in the year.
1st Elula-the beginning of the year in terms of the age of pets.

It is known that every tenth of this year Kosher for food for pets was transferred to the temple; This tithe was called Maaser Bhama. All animals born before the 1st Elul belonged to one year, and the Maaser had to be separated separately; All the animals born after the 1st Elul belonged to the other year, and their Maaser was already a tithe next year.
Animals born before the 1st Elul could not be transferred to the temple to redeem animals born after that date-and vice versa.
1st Tyshrea-the beginning of the year, which is the day of the court for the whole world; This day, a decision is made to whom life will extend for another year. In addition, the 1st Tyshrea is the beginning of the year in terms of the calculation of years ("sabbatical years", when the land is forbidden to cultivate, and the fruits growing on it are subject to special treatment) and Jovelus ("fifty year" when In particular, slaves were released, and land selected for debt was returned to their initial owners), as well as eagles (three years, during which it is forbidden to use young wood) and Maaserot concerning vegetables and cereals.
Thou-sewing is the New Year of the trees, the beginning of the year from the point of view of the separation of Maaserot from the fruits of fruit trees.

Maaserot (the parts of the crop transmitted to the temple, priests-Kogan, Levit, poor, etc.) were separated differently in different years. In the first, second, fourth and fifth years, counting from the last shmit, was separated by Maaser Shen (the "second tithe" - a tenth of the crop that had to be eaten in Jerusalem during the holidays); In the third and sixth years - Maaser oni (the "tenth of the poor", which had to be conveyed to the poor). All this is not counting the tubes (the parts of the harvest that was transmitted to the Kogan) and Maaser Richon (the "first tithe", which was transmitted to the Levita).
Since (as well as in the case of Maaser Bham) fruits belonging to one year can not "bring" at the expense of the crop of the other year, it is necessary to determine which day is the beginning of the year to calculate the maaserot of fruit trees. Torah determined that they have their own "New Year"-that Bi-Sew.
The fruits of fruit trees, which are tied to that bi-six, are considered fruits this year. The fruits that have been tied after that bi-sew will be considered fruits next year. The talmud is considered a fetus that has not yet reached a third of its normal size.
Our sages have installed the 15th sewing as a "New Year of trees", because to this day most of the annual rainfall falls, and the fruits have time to tie in the trees; Therefore, the fruits that will be tied after that day will become a "separate blessing."
The land to that bi-six is ​​already enriched with rain and winter holidays, so it is the best time to plant trees.