We celebrate the Dormition (falling asleep, or death) of the Theotokos today. She was told by the Angel Gabriel that her death was approaching and so she prepared herself. (Interesting note: Gabriel also announced to her mother Anna that she would conceive Mary and announced to Mary that she would conceive Christ.) According to tradition, the apostles were miraculously transported to her bedside so they could see her one last time and then serve the funeral service. Only Thomas (poor Thomas, I always think...) wasn't there on time. He arrived three days later and begged the other apostles to open the tomb so he could venerate her holy body. When they did, the tomb was empty with the exception of her sash or belt [which has been preserved down to this day and is kept in the Monastery of Vatopedi on Mount Athos.] By this sign the apostles knew that Christ had not only taken the soul of His most pure mother to heaven, but also her body. Of course, just as Thomas wasn't present with the other apostles when Christ showed Himself to them after His resurrection, this "lateness" too wasn't just carelessness on the part of Thomas but by divine providence, that we might see the works of the Lord and give glory to God.
In giving birth thou didst preserve thy virginity,
In falling asleep thou didst not forsake the world, O Theotokos.
Thou wast translated to life, O Mother of Life,
and by thy prayers thou deliverest our souls from death!
It is the tradition in many churches to bless flowers and "fragrant herbs" on this day.