The University of Missouri extension service has everything you need to know right here:
I've never heard the term "root" gladiola....hhhmmm? Mary, make sure you get them staked as many times the heavy flowers pull the stalks down. If you bought a variety of colors, it will be a wonderful display! There are winter hardy varieties that come back each year here in NY. I stopped taking them up for winter storage.
Thank you very much Mr. Hunt the website is very helpful !!! :-)