Provide a substrate that is easy for the frog to burrow in. Coconut husk fiber (bed-a-beast, eco earth, forest bed, etc.) or other safe soil is a good option. Soil generally holds moisture well, allows horned frogs to dig, and looks natural.
Do not use soil that contains vermiculite, perlite, fertilizers, or other unsafe ingredients. The moisture content of the soil is important, and it should never become waterlogged or completely dry. Moist paper towels or foam rubber can be used instead of soil, but must be replaced or washed frequently. Cypress mulch, sphagnum moss, and leaf litter are other suitable substrate options, although it’s recommended that frogs kept on these substrates be fed from tweezers or tongs to prevent them from swallowing a piece of bark or moss that could cause problems.
Do not use gravel, sand, or fir bark.
ref: https://answers.yahoo.com/question/i...0162747AAR6Ui5