Grow large onions by choosing the right variety, planting in the right location, preparing the soil, planting the seeds, watering the plants and fertilizing the onions. Use onion seeds, a garden trowel, compost and fertilizer.Continue Reading
Choose an onion variety that grows large bulbs, such as intermediate or short-day.
Choose a planting site that receives a lot of sun.
Till the top 10 inches of soil into a fine texture, breaking up any large chunks. Work 3 inches of compost into the top 6 inches of soil. Dig a long 2-inch deep trench, and sprinkle 1/2 cup of superphosphate fertilizer along it. Fill in the trench with dirt, tamp down the soil and water the planting bed.
Poke the onion seeds into the soil just above the fertilized soil. Make sure the seeds are no deeper than 1/4 inch. Cover the seeds with soil.
Gradually give the plants 1 inch of water over the course of a week.
Feed the onions with a granular 21-0-0 fertilizer every month by digging a trench and sprinkling it in the bottom of the trench. Do not apply the fertilizer directly to the bulbs, as this can burn them.