Root Vegetable

When to Plant Onions

The backbone of the kitchen garden. Choose short-day, intermediate, or long-day varieties based on your latitude.

Sun

Full sun (6-8 hours)

Water

1 inch per week

Days to Harvest

90-120

Difficulty

intermediate

Spacing

Frost Tolerance

high

The Short Answer

Onions are best direct sown when soil temperature reaches at least 35°F. Plant 4 weeks before your average last frost date. Enter your zip code on our homepage tool for exact dates.

How to Grow Onions

The single most important thing about growing onions is day-length type — get this wrong and your onions will never bulb, no matter how well you grow them. Long-day varieties (Copra, Walla Walla) bulb when days exceed 14-16 hours and work north of the 35th parallel. Short-day varieties (Granex/Vidalia, Texas 1015) bulb at 10-12 hours and work in the South. Intermediate-day varieties work in the transition zone. Starting from seed produces the largest bulbs; sets (small bulbs) are easier but often bolt before sizing up.

Starting Seeds Indoors

Begin onions seeds indoors 10 weeks before your average last frost date. Seeds need soil temperatures of at least 35°F to germinate, which typically takes 7-12 days. Provide 12 hours of light per day using a south-facing window or grow lights.

Transplanting

Move seedlings outside 4 weeks before your last frost date, once soil temperatures reach 35°F. Harden off seedlings for 7 days before transplanting by gradually exposing them to outdoor conditions.

Direct Sowing

Onions can be direct sown 4 weeks before your last frost date. Plant seeds 0.5" deep, spaced 6" apart.

Growing Tips

Day length triggers bulbing. Northern gardeners need long-day varieties. Southern gardeners need short-day varieties.

Companion Planting

Good companions:

Carrots Lettuce Beets Tomatoes

Keep away from:

Beans Peas

Onions Planting Dates by State

Click your state for onions planting dates specific to your location:

Alabama Alaska Arizona Arkansas California Colorado Connecticut Delaware Florida Georgia Hawaii Idaho Illinois Indiana Iowa Kansas Kentucky Louisiana Maine Maryland Massachusetts Michigan Minnesota Mississippi Missouri Montana Nebraska Nevada New Hampshire New Jersey New Mexico New York North Carolina North Dakota Ohio Oklahoma Oregon Pennsylvania Rhode Island South Carolina South Dakota Tennessee Texas Utah Vermont Virginia Washington West Virginia Wisconsin Wyoming

Note: Planting dates are based on average frost dates from NOAA Climate Normals (30-year averages). Actual conditions vary year to year. Always check your local forecast before planting frost-sensitive crops.

Last reviewed: March 29, 2026