For a crested gecko, you need something more sturdy than we usually use with the dart frogs. Pothos, Scindapsus, vining philodendrons, Chinese evergreen, Dieffenbachia, any of the ivies of the Hedera helix varieties, rooted in the substrate and grown around hardwood branches, will work. About 2 inches of gravel or LECA on the bottom for drainage, topped with a substrate of cocoanut fiber, or Bedabeast, kept damp or even wet, will grow any of these plants without additional fertilizers, and will utilize the gecko wastes, so you don't have to do "diaper changes" or strip your tank for years. A layer of long brown dried sphagnum moss on top of the substrate is even better. Sometimes it may "come alive" again and grow, which is even better. Maintenance is minimal, confined to necessary rinsing off leaves, misting if appropriate, and keeping the glass clean with a paper towel dipped in white vinegar, then dried off.
With dart frogs, we usually use more delicate plants, because darts are relatively small and don't tend to break and trample things, but I see no reason why a larger animal needs to hang around on stuff made of plastic. While the nice things like mosses and ferns might not survive well with a crested gecko--well, maybe they would, the tougher plants I've mentioned will do just fine. If you do try the mosses and ferns, if they die, you can always just remove them.
Some of the plants I mentioned are potentially toxic to an animal who ingests them. This is of little or no concern with most frogs or herps that eat insects, because they feed selectively, and unlike a cat or dog, don't just chew on stuff for the hell of it. Accidental ingestions are rare, even in the "gulp and gobble anything that moves" frogs. Darts never do this, and neither do any of the geckos that I know of.
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Patty
Pahsimeroi, Idaho
4 D. auratus blue
6 D. galactonotus pumpkin orange splash back
7 D. imitator
6 D. leucomelas
6 D. pumilio Bastimentos
4 D. fantasticus
6 P. terribilis mint and organe
4 D. reticulatus
4 D. castaneoticus
2 D. azureus
4 P vittatus
2 P. lugubris