I would recommend against using soil from the outside. It doesnt behave the same way once you get it in the tank and mostly it just tends to harden into a rock. Not really the best, I have kept mine successfully on Coco-Fiber, or Sphagnum Moss, both have done very well for me.

If you intend to breed your geckos, however, keeping them on this type of natural bedding will make that a little more challenging to find the eggs. They tend to dig and lay them where they feel most comfortable so you have to hunt for them.
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2.2.5 Crested Geckos
2 ringneck snakes
0.1 packman frog
1.1.1 Box Turtles
1 Redclaw Scorpion