big NO on crushed walnut as a substrate. This is about the worse substrate for dragons one can use. It is sharp edged, can damage the lining of the intestines and cause impaction.
Dragons under 10" do best on just plain paper towel. After that they can be put on a packed soil mix as Robin always talks about (see the 'I am Tired of Sand' post below).
For live plants, dragons don't need a bunch of plants for cover/security. A good basking spot and hide/cool area is all they need. If kept in a glass tank it often helps to cover the back and ends with white or black paper to give them more security (less distractions of things moving around outside the cage).
New dragons are good in simple cages till they get acclimatized, eating regularly and thriving. Too much cage 'clutter' tends to cause more problems than they are worth.
Keeping live plants in a bearded dragon cage is tricky. The plants at first, have to be non toxic as dragons tend to lick and nibble anything and everything in their cage. Also, the plants have to be strong and tolerate, capable of thriving in a hot dry environment and withstand a dragon crawling all over them or even uprooting them.
Cacti have their own set of potential problems. The spines can injure your dragon should he bump into it as well.
It is possible to set up a dessert/semi dessert vivarium with live plants and all that but this is advanced care and not for everybody.
If this is the first time you have owned a bearded dragon and/or first time owning any lizard pet, I suggest keep things simple. Get used to caring for a reptile before worrying about added complications and challenges. You can always move your dragon into a natural semi-arid vivarium tank with live planted or potted plants etc. for his adult cage. (4'x2'x16" minimum size).
There was an article in Reptile Magazine about a year or two ago about how to set up a dessert/semi arid vivarium. You may be able to find this article at their website.. www.reptilechannel.com I think the address is.
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PHLdyPayne