Welcome to the forum!! May we know your name and where you're from?
I just use whatever dirt is already in the area where my pens are going to go. I imagine if the dirt isn't any good you can import something, but outside just plain old dirt will do nicely.
Because you're new, I'll give you a helpful hint about posting. When you want to talk about something that is already being talked about in a thread, then you will put your post in that person's thread. If you have a new question that doesn't pertain to the original thread or post, then you need to start your own thread.
Glad to have you here on the forum with us. We need more Russian keepers!!
on tula's outdoor enclosure i just put some fencing in and left the dirt right where it was. i did buy a few bags of topsoil from lowe's but that was because it sloped a little bit in her pen. but i will say, that topsoil really was better than the dirt i already had in there, the plants that i planted in the topsoil just went crazy, i would swear by my rose bush doubling in size.