How to Grow an Onion Set

Onion sets are tiny onion bulbs ready for planting.

Onion sets refer to the tiny marble-sized onion bulbs sold to grow onions in the garden. Although, onions can be started from seed, growth is slow and they rarely reach maturity in one season. In fact, onion sets are produced by planting onions by seed and harvesting the tiny bulbs in the fall. These "sets" can be stored for the winter and planted in the garden in the spring to produce mature onions in the second year.

Things You'll Need

• Garden tiller
• Compost
• Well-rotted manure
• Garden rake
• Fertilizer, 10-10-10
• Garden hoe
• Organic mulch, hay or straw

Instructions

1. Select a location that receives six to eight hours of direct sunlight a day. Till the soil to a depth of 8 to 12 inches. Spread a 3- to 4-inch layer of compost or well-rotted manure over the area and till it in well. Rake the area smooth with a garden rake.

2. Spread 1 to 1 1/2 pounds of 10-10-10 fertilizer per 100 square feet and till it in with existing soil.

3. Plant onion sets in the spring once the soil temperature has reached 48 degrees. Position the sets with the pointed end up to a depth of 1 to 2 inches, spaced 2 to 4 inches apart. Cover the onions with soil and firm the soil down with your hands to secure the bulb. Space rows 12 to 24 inches apart.

4. Water to moisten the soil to a depth of 2 to 4 inches. Keep the soil moist until green shoots appear. Reduce water to once a week, or whenever the soil feels dry 1 inch below the surface. Water deeply to saturate the soil to the root level.

5. Sidedress the onions with 1 pound of fertilizer per 100 feet of row, approximately four weeks after planting the onion sets. Create a thin band of fertilizer 3 inches from the row of onions and work it in with a garden hoe. Use care not to disturb the roots of the growing onions.

6. Control weeds by pulling or cutting them at the ground level with a hoe. Organic mulch, such as hay or straw, layered 1 to 2 inches to prevents weeds and keep the soil cool.

Tips & Warnings

• Onions mature according to the length of daylight. Choose long day onions if you live in a northern climate and short day onions for southern area.

• Small onion sets typically produce the biggest onions, whereas, larger sets tend to mature quickly without forming a large bulb.

• Do not add lime to gardening areas where you intend to grow onions, as they prefer slightly acidic soil.

References

• Iowa State University Extension; Onions; Cindy Haynes, et al.; 2009
• Minnesota State University Extension; Growing Onions; Beth Jarvis; July 2001

Resources

• AgriLife Extension: Onion