Rose wedding bouquets pull a lot of water from the foam. Be sure to choose a large enough holder and replenish the water if needed by holding it under a trickle of water from the faucet. Choosing the right bouquet holder is important, because roses need a constant water supply to stay at their peak of freshness.. I generally use a Grande holder unless it's a very small bouquet.
Treat the water with a flower food. This is important. You can't use too much - it will not hurt the flowers. But it is a waste of product, so follow the directions on the bottle carefully.
Allow the bouquet holder to "float soak". Do not push the dry foam underwater. This can cause dry air pockets that can mean death to a flower head or two. It only takes a short time for the foam to fully saturate.