Learning how to correctly use florist supplies is always "basic 101" in professional flower shops. Watch a quick demonstration on how to correctly "block in" wet foam in flower containers.
It's important to leave a couple inches of foam ABOVE the container so you can insert flowers and greenery laterally.
If foam does not seem wedged in tightly, you may want to use waterproof tape that florists use to secure odd blocks of foam into containers.
Remember that the foam (which contains the water) is the life of your fresh flowers. Trying to skimp on this inexpensive product means that the flowers can suck the water out of the foam quickly, leaving them dry and on the way to wilting.
Always be generous with the foam so it can properly support a large amount of flowers. You'd be surprised just how much water a dozen or more flowers can drink each day!
The new MaxLife foam by Oasis mimics the cell structure of fresh flowers and has been proven to actually extend the life of some flowers longer than a vase of water!
Don't forget the flower food! Especially developed for fresh flowers, follow the instructions on the container for correct usage. I can't stress enough that for a large investment in fresh bulk flowers, it's worth going a little more and buying the professional products designed to keep those flowers at the peak of freshness.
I have a step-by-step guide on how to correctly process fresh flowers that are bought online. It's worth a few minutes read if you plan on doing your own wedding flowers.
Check out a wide variety of waterproof containers, ranging from utility (cheap and disposable) to nicer finishes appropriate for wedding work. They are guanteed leakproof and many container spikes on the bottom to help grip the foam tightly into the container.