Most tropical plants found at your local plant nursery of garden center should work well. Some hardware stores have a good selection as well. For tree frogs select plants that have sturdy leaves so that they can support the weight of the frog if they jump on them. I have a list of plants I have used in terrariums that have worked well at www.amphibiancare.com/frogs/articles/tropicalterrarium.html Wash the plants off very well with warm water before placing them in the cage to rinse off any chemicals that have been sprayed on them.
Most aquatic plants sold at pet stores for aquariums will work well for newts but, once again, you might want to select species that have sturdy leafs so that the newts can perch on them underwater. I would caution you against housing the newts with the tree frogs. Good luck,
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Devin Edmonds
devin@amphibiancare.com
www.amphibiancare.com