Have submerged them before, and they seemed to last pretty well. To be on the safe side I did add a small amount of flower food to the water (making sure the water went clear). l think they will definitely last the duration of a wedding...I have some at the moment so will get one submerged again and see if it does as well as the last time...will give it 12 hours and check it, will try and get back to you tomorrow and let you know the result!!