Tu B'Shevat is February 3rd, 2015
Tu B'shevat is considered the Jewish New Year of Trees. Trees are extremely important in Judaism: trees are used metaphorically to consider G-d and life in Judaism and the planting of trees is holy. Combine that with the very modern importance of reclaiming the barren desert of Israel through planting trees, and it's easy to see why a celebration of trees is part of our tradition.
THE ORIGIN OF TU B'SHEVAT
The Jewish New Year of Trees was originally the date Jews used to calculate the age of trees. A tree is as old as how many Tu B'shevats it has been on Earth. Why is this important -- to calculate the age of trees? Well, there is a Commandment in the Torah that people shouldn't eat the fruit from trees for the first four years: no one eats for the first three and then during the fourth year the fruit is picked but not eaten (instead is donated to "G-d"). Then after the tree reaches four years of age, people can eat the fruit. Go ahead and ask "why four years?" but there is no good answer except "it is Commanded."
The Tu B'Shevat seder began as a Kabbalistic Jewish mystical practice in the 17th century. Ecologically minded Jews have adopted Tu B'shevat as a time to honor conservation and sustainable agriculture. The seder pretty much consists of drinking wine, eating fruit, praising G-d for creating these things, and reminding ourselves that we are stewards of the Earth.