To grow onions, plant the seeds or onion sets directly in the garden, and provide the plants with well-drained soil, water and fertilizer to promote growth. Most onion varieties are fully mature about 60 to 110 days after planting.Continue Reading
Sow onion seeds directly in the garden when the soil reaches 50 degrees Fahrenheit, or plant onion sets two to four weeks before the final frost of the season. Thin the seedlings to one plant every 3 to 4 inches to grow full-sized onions; space smaller varieties, such as cocktail onions, 1 to 2 inches apart.
Onions thrive in well-drained soil and require weekly watering. Add a layer of mulch around the base of the onion plants to retain moisture and prevent weeds. Onions benefit from the application of a nitrogen-rich fertilizer several weeks after planting and at regular intervals throughout the growing season. Protect the plants from temperatures below 40 degrees Fahrenheit to prevent bolting.
Onions are ready to harvest 60 to 110 days after planting, depending on the variety planted. When the top of the onion falls over, the plant is ready to harvest. Store the onions in a cool, dry location after harvesting.