Most plants don't do well in bearded dragon tanks. They tend to get uprooted, trampled and sampled, or completely eaten. The hot dry conditions is tough on most plants too. You also want to avoid cactus as dragons can injure themselves on them.
River rocks, drift wood etc are all great decorations to add into a tank. Fake plants can be added to but again watch to make sure your dragon doesn't try to eat them. For any 'natural' decoration, make sure they are washed and disinfected (either baked in the oven at 250F for several hours or soaked in bleach/water mix (1/10) for 20 minutes then rinsed really well, then rinsed several more times again and allowed to air dry for 24 hours in a well ventilated area).
Store bought river rocks and wood can just be washed and dried and soaked with a weaker bleach solution or washed with other disinfecting cleaner, such as Novasan (or however its spelled).
If you do want to keep some living plants in your dragons cage, I suggest you get a few plants of the same type, keep them potted and rotate them in and out of your cage every week, this way each plant has time to recover.
All store bought or nursery bought plants should have the soil they came in replaced with clean potting dirt free of any insecticides etc. Give the plant a week with normal waterings etc so any toxins on or in the plant from chemicals can be washed out. Then they can be used in the tank with your bearded dragons safely.
Below is a link to a list of safe plants to put in dragon's cages. The link also shows a great list for greens and fruits safe for dragon consumption as well as how frequent if ever, each can be fed. Below this list is the list of the plants.
www.beautifuldragons.503xtreme.com/Nutrition.html
If you see a plant not on the safe list that you are thinking of putting in the tank, ask here first. If there is any doubt, better not to put it in the cage. The plant can't hurt your dragon if he can't get at it and he won't suffer at all if no plants are in his cage for decoration. 
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PHLdyPayne