Yes, Epsom salt is a great natural fertilizer for Christmas cactuses. Epsom salt is high in magnesium, which is an essential nutrient for healthy plant growth. By providing the plant with magnesium, you can help it grow stronger and healthier. It also helps the soil retain moisture, which is important for the plant's survival in dry conditions. To use Epsom salt, simply dissolve it in water and pour the mixture into the soil around the plant. You can do this every few months for best results.