Select a staghorn pup to cut from your mother staghorn fern. There should be at least a small gap between the living, or green, parts of the main fern plant and the young fern you wish to separate and remount. The selected pup should have at least two green fronds growing from it.
Water the mother plant thoroughly. This will reduce stress to both ferns once they are separated and will ease the cutting process.
Cut the sterile -- brown -- fronds connecting the parent plant to the new pup, leaving an equal distance between the two plants.
Soak the sphagnum moss in water before using it. You will only need a couple of handfuls of the moss, enough to equal the diameter of your pup plant and create a buffer of 3 to 4 inches between the plant and your plank.
Attach the sphagnum moss to the bottom of your new staghorn fern using fishing line to ensure the two are connected securely.
Place your staghorn fern on the wooden plank. Make sure it is oriented in the same direction as it was when still connected to the mother plant.
Secure, or graft, your staghorn fern to the wooden plank with more fishing line.
Hang the newly mounted staghorn fern outside where it receives four to six hours of sunlight each day.