plants
All about plants and their use
Many people ask if they can put a plant in their dragon's cage. Honestly, the environment wouldn't likely support a single plant and your dragon will end up stumbling around on it or just knocking it over. If you're wanting to do something like that, I'd look into bioactive enclosures. There's a few good bioactive groups on facebook that you could seek out. A bioactive setup would be the only type of setup where I'd recommend having live plants.
Safe plants
As far as feeding plants as treats, there are safe options. Some of the most common choices include the following:
Alfalfa
Basil
Clover
Dahlia
Dandelion
Hisbiscus
Lavendar
Maple
Mint
Oregano
Petunia
Rose
Rosemary
Sage
Squash
Thyme
Zucchini
Not safe
The main plants that have been shown to be toxic to dragons and shouldn't be fed at all (its not even worth the potential risk):
African Lily
Arrowhead Vine
Avocado
Black Locusts
Bleeding Hearts
Bloodroot
Boxwood