It was a tradition in our Irish family. It was the one thing that I asked my daughter to do at her wedding.
Sarabande has given a good explanation. It use to be only the bride who said a prayer and presented flowers by the time I was married they were encouraging couples.
I found this
Devotion to The Blessed Virgin Mary - (Tradition)
Mary, the mother of Jesus is the ultimate role model for the Catholic bride, as she will strive to mirror Mary's perfect love for God and devotion to her family. Brides often wish to seek the guidance and blessings of The Lord, through a ceremony that requests the intercession ( to request on your behalf ) of the Blessed Virgin Mary, through prayer and the laying of flowers.
In some areas of the country this devotion will be requested to be included in the marriage ceremony and most Catholic guests will be familiar with it. In other areas of North America this addition to the ceremony is not prevalent. Devotions to The Blessed Virgin Mary have always been present in the Catholic faith, however they are not officially included in The Rite of Marriage.
The church will never discourage your personal devotions, however the wedding ceremony is seen as a time of inclusion and participation of your guests. if you are requesting to have The presentation of Flowers to Mary , carefully plan this additional portion of the ceremony.
As the ministers of your ceremony, you must strive to avoid any feeling of separation from the unity with your guests In the midst of your wedding ceremony. Including a Hymn or prayer that the entire congregation can sign or say, while you are laying your flowers, would be a way of including your guests.
For those areas of the country where this custom is not the norm, including a short explanation of this addition to your ceremony would also be helpful to both your Catholic and Non-Catholic guests.
For those who desire to have a more private act of prayer you may request a more intimate opportunity, such as before or after the wedding rehearsal. In order to permit time, this request should be made well in advance to your parish priest.
I think you might find this to be useful
Usually the bride and groom will bring a flower to lay next to the statue of Mary and ask for your guidance and intercession (not mediatorship, but intercession--which is pleasing and acceptable to God--1 Tim 2:1-2).
Many couples decide to do this because we recognize that Christ's first miracle was at a wedding feast. It is because of the Blessed Mother that He performed this very first miracle for the bride and groom.
She came to Him and told Him that they were out of wine, understanding that He had the power to keep the couple from being embarrassed and ridiculed by their lack of wine (which would've happened by the Jewish belief). When He said "It is not my time", she answered Him by telling the servants to do whatever He said. She knew because she asked, He would do this and He did.
That is all this is. It's a very nice gesture to our Heavenly Mother (as Jesus is our Brother and God is our Father, therefore Mary (the Mother of Christ) is our Mother as well).
You don't have to do this...but I would talk it over with your husband to be.
When I got married, we didn't do this because my husband didn't like the idea as he wasn't Catholic. I still wish I could've laid a gift before her, but I asked for her intercession anyway.