The fact that they dried out means you don't have nearly enough moisture in there. Definitely try covering a good portion of the enclosure. Adding water to the substrate. You could try growing herb plants. Your tortoise won't eat them probably but they make good cover. Sometimes you can find them at grocery stores even and they don't have pesticides because they are made for human consumption. It's going to be much easier to put establish plants in there been trying to grow any in there. Or do you have any friends with house plants that don't have chemicals? Or yard plants that don't have chemicals? I got a great spider plant from somebody that is growing like crazy. And I do not have a green thumb at all so if I can grow it anybody can.