"...a land of wheat and barley and (grape) vines and fig trees and pomegranates, a land of olive trees and (date) honey"
On Tu Bishvat it is the custom to eat a "new fruit", one that you've not eaten in the past 12 months. The custom is to eat fruits from the seven species for which the Land of Israel is praised. It is customary to eat a new fruit from the Land of Israel of which one had not yet partaken the present year, so that a Shehecheyanu may be said.
Our Sages have designated the 15th of Shvat as the boundary between one year and another, since most of the rains of the previous year have already fallen. Any new growth of fruit after this day is a result of the blessings of the new year. On the 15th of Shvat also, the soil is already saturated with the rains of the previous winter, so that trees newly planted after the 15th of Shvat are assured of taking firm root and giving fruit.
The 15th of Shvat is one of the four Rosh HaShanahs (New Years) which each year contains. The 15th of Shvat is the Rosh HaShanah of trees, with reference to the different tithes, which are brought each year, counting towards the seventh, Shmitah year. The same applies to the conclusion of the Orlah years. And some hold that it also applies to the fruit of the seventh year, so that fruits, which begin to ripen before the 15th of Shvat of the eighth year, have the status of fruit of the seventh year. Fruits are regarded as having begun to ripen from the time of their appearance, but prior to having reached a third of their full size.
What does that mean, "New Year for the Trees?" The Torah teaches that everything in this world was created for the sake of mankind. Which means that "New Year for the Trees" is in some respect a "day of judgement" for each of us as well. In fact, the Torah in various places compares a person to a tree:
Tu Bishvat is the day of the year when trees stop absorbing water from the ground, and instead draw nourishment from their sap. This is significant in terms of Jewish law because fruit which has blossomed prior to the 15th of Shvat could not be used as tithe for fruit which blossomed after that date.
A person whose wisdom exceeds his good deeds is likened to a tree whose branches are numerous, but whose roots are few. The wind comes and uproots it and turns it upside down. But a person whose good deeds exceed his wisdom is likened to a tree whose branches are few but whose roots are numerous. Even if all the winds of the world were to come and blow against it, they could not budge it from its place.
(Pirkei Avot 3:22)
"It is a tree of life for all who grasp it"