oh, I see. You're in Iowa, were blest in the Midwest. You can use almost any hardwood branch, as long as it's old, dry, barkless, or 1/2 rotted. Half rotted ones, use a stone and scrub off all the rot. These make a nice Malasian looking wood, with dark and light tones. Bake for one hour at 200 degrees to kill possible chytrid. I use all natural wood in my vivs.

Just no pine or anything weird, oak, iron, hickory, birch, etc are all fine