Cranberries are a staple of the holiday table, but few of us know them other than as a relish or jelly. Keep these native fruits in view by using them as a flower frog instead of pebbles or marbles; they will hold stems in place for about a week. Use hard cranberries; wash them well before submerging in water.

Cranberry Flower Frog
Russell's Saturday Centerpiece
Beautiful and Lovely!
Works just fine if you fill the vase with cranberries. They can't act as a frog if they are floating.
Maybe you can keep them from floating by first placing the cranberries and flowers in the vase then add water using a watering can :)
I just did this for a party and mine did float. I think the key must be having enough cranberries which I did not! It still looked pretty but was more like a band of red in the vase with water on the bottom and the the flowers on top.
How do you keep the cranberries from floating?
How do you keep the cranberries from floating?