You can use straight plantation soil or even a mix with coco fiber, jungle mix or so on.

I love the Zilla Jungle Mix but since tree frogs are pretty aggressive eaters I would go Plantation Soil.
I use Jungle Mix with My Whites but its covered with coco fiber and plantation soil. The Jungle Mix holds moisture well and thats great for keeping humidity up.

Look at my photo albums and check out the 20 gallon tank pics for how plants for in plantation soil and Jungle Mix.

Might give you ideas for putting that Brom in a cork round for support or on a wall and looks cool too.