HCA: Hermit Crab Association

I've seen some people put small planters in their crabitat to grow sprouts or other plants that are edible to the crabs. I'd like to grow something like moss, or maybe some sprouts, but I was wondering what growing medium would be safe for hermit crabs. Like, is there a kind of potting soil that wouldn't hurt them? Or should I plant in dried sphagnum moss maybe? Or just put some live moss in the planter I have? (it's a little terra cotta pot, maybe 3 inches tall, with a hole at the top and also extra holes on the sides that have little ledges on them, which would be great for the crabs to climb and forage in I think.

Update!

I decided to use cocoa fiber! I put some cholla wood in the planter to give them something new to climb, and I'm gonna plant some seeds in it when I get some! Here is the end result:

That looks awesome! What kind of seeds did you plant? It’s been a few months now so I’m wondering how it worked out?

That looks really cool! I hope your hermits crab like it The cholla wood was a good idea