The month of May is dedicated to the Blessed Virgin Mary. We set the month apart by presenting flowers and crowning her. We also sing special hymns and anthems which honour her throughout the month. The practice of dedicating the month of May to our Lady was popularized especially by Pope Leo XIII in the latter part of the 19th century, but the idea goes back to ancient times.
In classic western culture (both Greek and Roman), May was recognized as the season of the beginning of new life. In the Greek world, May was dedicated to the goddess Artemis, and although that cult was riddled through and through with immoral practices, it did establish a relationship for the month of May with fertility and motherhood. Roman culture linked the month of May to Flora, the goddess of bloom and blossoms, and this led to the custom of "ludi florales" (or floral games) which took place at the very end of April as a preparation for entering into the month of May.
It seems that this ancient tradition of connecting May with new life and fertility, led to a realization that May is very much the month of motherhood and likely is one of the reasons why Mother’s Day is celebrated during May not only in the United States but in many countries and cultures of both the East and the West. In the month of May, the winter comes to an end and the spring season begins. In fact the month of May was the official beginning of spring in Roman culture.
The connection between motherhood and May led the Church eventually to adopt May as Mary’s Month. May is the Month of our Lady precisely because she is the Mother of God and our mother, too.