You might already know how to make gladioli last a long time, but I learned something new this week. This is info straight from the vendor at the market who sells these flowers and nothing else: if you want gladioli to last a long time the trick is to use ice cubes. Change the water twice a day and each time, add some ice cubes. Cut the base of the stems once a day. Keep out of full sun. The flowers will open slowly and last all week. I bought these on Saturday and they were completely closed but this method seems to work as predicted.