My substrate of choice is orchid bark. In the hermanni care sheet that's pinned at the top of our Hermann's section, here on the Forum, the author, Chris, says, "A suitable substrate is clean top soil mixed with coconut coir or peat moss. I prefer to ad sand into this mix to help generate a substrate that replicates what they experience in nature more closely. However, using sand has been known to cause impaction in reptiles which can lead to death. Although in more than 20 years we have never experienced this with any of our tortoises kept on it, this does not mean it won’t happen to your animal(s). Use caution or simply don’t use the sand. The substrate can be up to 4” deep to allow for burrowing. Burrowing is 100% normal! Do not be alarmed by his behavior while they are this young. They are babies after all and babies sleep. I also recommend adding cypress mulch as a 2” top layer but you can also mix it in to the existing substrate. The mulch aids in keeping an adequate humidity level which should be around 70%. Do not let the substrate dry out entirely by keeping a spray bottle filled with water on hand to mist the enclosure. A common misconception regarding tortoise keeping is thinking they must be kept very dry. This is in fact not true and we now know that pyramiding (unnatural, lumpy growth of the carapace scutes)is directly linked to improper humidity levels along with insufficient hydration. In nature, baby tortoises spend a great deal of time burrowed into the ground, under leaf litter or jammed under debris. There, it is humid, moist and dark. They are programmed to hide and typically do not venture out anywhere near as much as older specimens. By doing this they are constantly subjected to a higher level of humidity than one might assume. Although wild tortoises can sometimes appear lumpy or pyramided, this is only in extreme cases where severe droughts are common. Most will exhibit beautiful growth and smooth shells. In the evening after the lights are turned off, I place the lid on the rubbermaid containers that house our baby tortoises. This helps to mimic the dark, humid refuges the neonates confide in when in nature. The humidity builds up overnight and in the morning it is released when the lids are taken off. I do not doubt for one second that this method has something to do with the natural, smooth shells our tortoises attain as they grow. "
I use 4 inches of organic potting soil. It compacts well in the areas she walks, but is soft enough that she can bury herself and snuggle in! I also transplant plants into it, and she loves to dig a resting spot under their roots.