I have a large sago plant in my front garden, the edges of the leaves are curling and turning yellow. The rest of the leaves are f
ine and green..why
The most likely reasons are water deficit, or fertilizer burn from high salts content in chemical fertilizer . Either of these will cause drying of the tissues at the leaf margins.
Check on your soil moisture and water management. Using a soil moisture meter may help. Discontinue use of any fertilizer with NPK percentages of over 10, best to use a slow release natural fertilizer.