Time of the Year to Transplant Onions

Transplanting Benefits

• In home gardens, it is best to start the seed indoors and then transplant seedlings outside, suggests the University of Minnesota Extension. This offers several advantages, including having transplants ready as soon as it is planting time and a greater selection of varieties. Growing transplants at home is also more economical than purchasing.

Starting Transplants

• The recommended time to start seeds indoors is 8 to 12 weeks before the earliest spring planting time in the area. If usual planting time is April in your area, start seeds indoor during January. Do not buy excess seed, because onion seeds are no longer viable after a year. When selecting varieties, choose according to the location. The long-day onions are best suited for the North while the short-day varieties grow optimally in the South, as cited by the University of Illinois Extension.

Transplanting Time

• The time for transplanting onions differs by region. Check the ground in spring for tillage. As soon as the soil can be worked, start transplanting the vegetable. This is usually between late April and early May in the main onion producing areas in the United States. Avoid planting too early because the young onion seedlings or transplants are very sensitive to cold soil.

Planting Tips

• When transplanting, plant to a knuckle-deep depth -- about an inch. Make sure all the roots are completely covered and the crown is partially covered with soil. Space the plants about 4 inches apart. Amend the planting hole with phosphorus, 0-20-0 fertilizer, prior to planting because this greatly improves growth. After plants are established, apply 21-0-0 fertilizer once every three weeks at the rate of a pound per 100 square feet. Plant onions in areas of full sun for best growth.