1,256. Reasons to Declare a Leap Year

Hilchos Kiddush HaChodesh 4:2

The year is made full (i.e. a leap year) because of three things: the vernal equinox, the ripening of barley and the blossoming of fruit trees. The court makes calculations in order to determine when the vernal equinox will fall. If it will be on 16 Nisan or later, the year is made full. The month that would have been Nisan becomes Adar II and Passover falls in the spring. This is reason enough to make the year full without any other considerations.

Hilchos Kiddush HaChodesh 4:3

Similarly, if the court sees that the barley has not yet ripened because it is sprouting late, or that the fruit trees that normally blossom at Passover time have not done so, these considerations are enough to declare the year full even if the vernal equinox will fall before 16 Nisan. These things are important enough to warrant declaring a leap year in order to ensure that there will be barley available for the omer offering that is brought on 16 Nisan and that fruit will blossom in the spring as per usual.