How to store onions at home to avoid spoilage for several months?

Onion stores well only if you start with the right bulbs and cure them properly. Use a storage type variety harvested at the right maturity, with the necks falling over, not over-irrigated late. Cure the bulbs first by drying in shade with good air movement for a couple of weeks until the outer skin and neck are fully dry; this is the single biggest factor against rot. Avoid washing, bruising or cutting the bulbs. Store in a well ventilated structure where air can move through the heap from below and the sides, not in closed sacks piled on the floor. Keep the layer or stack height moderate so the bottom does not get crushed and heat up. Keep it dry, shaded and cool, away from rain and direct sun. Sort regularly and remove any soft, sprouting or rotting bulbs so they do not spoil the rest. Doubles, thick necks and bruised bulbs do not keep, so sell those first. With good curing and ventilation, storage life improves a lot, though it still varies by variety and season. Verify the best storage variety and curing period for your area with your local horticulture office or KVK.