Are Epsom salts a good fertilizer for sago palm trees?

Yes, Epsom salts can make a good fertilizer for sago palm trees (Cycas revoluta).

Specifically, Epsom salts contain magnesium sulfate. Sago palms may suffer from magnesium deficiency. Judiciously applied Epsom salts work to correct the deficiency with the injection of magnesium in a form that can be taken in by sago palm tree roots.