I would think about using the watergel crystals (and maybe some of the snow!) instead of dealing with the messy real ice. Here is a link for the gel and the snow:
water gel crystals and snow

Put the gels in clear glass rose bowls (to kind of look like icy balls or snowballs) then add in your fern. Set this on a clear plastic plate and scatter some snow on there. You might even get some of the snow spray and the ultra fine glitter and touch the ends of some of the fern fronds with that for an icier feeling. Some thing birch or other gathered twigs spray painted white and touched with some glitter would be pretty rising out of the center of the fern, too.

You could use an icy blue paint pen to write "Have a cool summer!" several times around each rose bowl.

How about using glass blocks?

I like both of these ideas. The faux snow might be beyond my skimpy budget. That's why I was going towards freezing water and flowers -- they're free. I like the glass blocks idea, and I've seen on this forum the beautiful ones that can be made. I could afford the $4 each, but would they look dramatic without a light inside? One winner at each table gets to take the centerpiece home, but I might still would consider glow-sticks, which would be cheaper than battery lights and cooler than a candle, but not last beyond the day of the party.

Anything else come to mind when I say COOL? Polar bears. Penguins. Icicles. Maybe it's because the Christmas season's just behind us, but I'm staying away from snowmen and other winter holiday themes. It'll be June and I live in the south. Each lady will get mints in a clear cellophane bag tied with a ribbon that indicates menu choice to the wait staff. I'm still open to other ideas for table decor or centerpieces.

For summer 'cool', I think lemon slices (or lime) and mint.
Maybe you could do something like the 'captured lemon vase' on this commercial site.

Here is a link that might be useful: captured lemon vase

Hello;

I have done this a couple of ways. Get a large mixing bowl and put a smaller bowl inside of it and between the 2 put roses and ferns and water, Freeze and this makes a great fruit salad bowl. There is no reason why you could not put water in the middle with a floating candle or even place a candle in the middle without the water. IT WILL NEVER REACH THE ICE IN 2 HRS. They also have those pretend candles now and they flicker like real ones.

The other thing I did was a cylinder like a paint can and put in orange slices, greenery, cherries and freeze with a quart size Heninz 57 vinegar bottle in the middle then freeze, and put inside of the space a bottle of wine or once again a candle.

People love this too. Enjoy!

Go to GOOGLE and type in acrylic ice cubes...there's a slew of places you can get them wholesale priced..even lighted ones!! One place has bags of fake ice in chips-sold by the pound. You might get some ideas for using them. You might even consider using the clear plastic stemmed goblets, place 1 lighted ice cube in the bottom of the glass & top with the ice 'chips' The color should shine up thru all of the chips. Then tie a ribboned tag on the stem saying "Think Cool" or whatever saying you prefer-would make great favors for everyone! OR...get some fishbowls and make one for each table in a larger version of the above idea.