We are getting an unexpected blessing on Tuesday, a Russian tortoise! He is an adult. We found out tonight and started on his 4x8 outdoor enclosure. We are attaching welded wire to the bottom, adding six inches of digging dirt for him and then adding more height to his enclosure and putting a top with welded wire on top to protect him from predators. I’m placing it half under a very shady tree and the other half in full sun. Flower pots will be in it for cool hiding spots. I have some seeds for tortoises ready to plant. Question, what type of dirt should I put in it for his substrate? I need to get a lot done tomorrow.