Blend equal amounts of sterile, coarse sand, leaf mold, peat moss and loamy soil, which is potting soil amended with organic matter. Add a handful of charcoal chips to the mixture to keep its pH alkaline. Plan to replant the staghorn fern in the spring.
Add some of the potting mix you prepared to the bottom of a planter with drainage holes. Select a pot that is just large and deep enough to accommodate the root system without much room to spare.
Take the fern out of the pot it is currently in. Place the root system on the layer of soil in the new planter. Adjust the potting mix thickness at the bottom as needed to position the staghorn at the same depth as it has been growing.
Water the staghorn fern until excess moisture drips from the drainage holes. Wait until the soil feels dry and the foliage begins to wilt to irrigate it again.