Yes, Epsom salt is a good citrus fertilizer. It's high in magnesium and sulfur, two nutrients that citrus trees need for healthy growth. Adding Epsom salt to your citrus tree's watering can help improve its health and yield larger, juicier fruits.
To apply Epsom salt, mix one tablespoon of salt into half a gallon of water. Apply the solution to your citrus tree's roots once every two weeks. Be sure to follow the package directions for the best results.