All Answers

well it all really depends on what type of flower your using... there are a lot of flowers out there that if you just pop the head off it will float on its own...

Just snip the heads with as little stem as possible, it will float

I use 2 inch thick Styrofoam, cut it ina 6 inch circle,cover it with tea leaves to hide foam. Secure the laves on the bottom with greening pins or regular pins.Use Floral water picks -use about 3 flowers and pick it into the center cover tubes with Spanish moss at the base. You can call me at my Shop-650-591-0751
Granara's Flowers..ask for Robin

There are some easy float options available. thin closed cell foam sheets ( not foam core) available at craft stores can be cut in any shape and you pop the flowers stem cut short into this as a "Collar" this keeps the fllower from getting water logged and it should float all day.

If placing in a fountain or pool the filter needs to be turned off or they will all blow to the filter and look funny.
we add fishing string with weights to keep pool flowers in place, but its not a DIY job for a wedding party member, leave that to the pros!

You don't need anything to help the flowers float in a vase, they naturally float. Just cut as much of the stem off that you can and the head will float. You do, however, to choose wide, more flat blossoms for a prettier effect. Gerbera daisies, open roses and orchids all work beautifully. Pick up a couple of stems before your wedding to experiment with.