Romain, celery and kale should not be fed as a regular diet. Romain is nutritionally worthless, and can give them diarhea, celery and kale should only be fed occasionally. Kale in particular can bind the calcium in their systems.
Better choices would be collard greens, dandillion greens, mustard greens, turnip greens, any type of squash. Any of those would be excellent staple veggies, escially a variety of them offered daily.
Here is a website for what you can and can't feed.
http://www.beautifuldragons.com/Nutrition.html