Why May is Mary's month

"The mood of springtime informs the church's interior;
nature's blossoming, the warm air of May evenings, human gladness in a world that is renewing itself -- all these things enter in.

Veneration of Mary has its place in this very particular atmosphere, for she, the Virgin, shows us faith under its youthful aspect, as God's new beginning in a world that has grown old.

In her we see the Christian life set forth as a youth-fulness of the heart, as beauty and a waiting readiness for what is to come."

SOURCE: Joseph Cardinal Ratzinger, "Seek That Which is Above"
(This new film on the Apparitions at Fatima looks promising: the 13th day for the trailer.