How cool is this!!!
This is similar to the unity candle and sand mixing ceremony...
The bride and groom plant a tree (or flower/plant) together!
Have a small tree in a pot and then have the bride and groom both add soil.
Mothers/fathers/parents can come up and add water to the tree to symbolize parental guidance over the couple and their commitment to helping the relationship "grow." After the wedding, the bride and groom can take the tree home to plant in their yard and watch it grow over the years. Everytime they look outside their window they will be reminded of the vows they made to each other.