Root Vegetable

When to Plant Onions in Hawaii

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

The Short Answer

In Hawaii, soil conditions are an important factor for onions. Volcanic soils — extremely fertile but can be acidic. Excellent drainage on slopes. Varies dramatically by island and elevation. Direct sow 4 weeks before your last frost date.

Hawaii Frost Dates

Your planting dates depend on which part of Hawaii you're in. Here are the frost date ranges by region:

Region Zones Last Frost (Spring) First Frost (Fall)
Coastal Hawaii 11a, 11b, 12a, 12b, 13a None None
Upcountry/Mountain 10a, 10b, 11a Rare Rare

Onions Planting Schedule for Hawaii

Coastal Hawaii (Zones 11a, 11b, 12a, 12b, 13a)

Average last frost: None · Average first frost: None

Start Seeds Indoors
10 wks before frost
Transplant Outside
4 wks before frost
Direct Sow
4 wks before frost

Upcountry/Mountain (Zones 10a, 10b, 11a)

Average last frost: Rare · Average first frost: Rare

Start Seeds Indoors
10 wks before frost
Transplant Outside
4 wks before frost
Direct Sow
4 wks before frost

Growing Onions in Hawaii

Onions in Hawaii's Climate

Short-day onions only. Plant transplants from October through December for spring harvest. Short-day varieties like Granex (Vidalia type) and Texas 1015 bulb when days reach just 10-12 hours — perfectly timed for your spring. Do not plant long-day or intermediate varieties — they will never bulb in your day-length pattern.

Soil Considerations for Hawaii

Volcanic soils — extremely fertile but can be acidic. Excellent drainage on slopes. Varies dramatically by island and elevation. Loose, well-drained soil is especially important for onions since the edible portion grows underground. If your soil is heavy clay, consider raised beds.

Hawaii Climate & Growing Season

Tropical. Year-round growing season at lower elevations. Elevation creates microclimates. Plant warm-season crops anytime. Onions can handle frost well, which is an advantage in Hawaii's climate. You can push planting dates earlier in spring and extend into fall.

Growing season length varies across Hawaii: Coastal Hawaii (11a, 11b, 12a, 12b, 13a) has a last frost around None, while Upcountry/Mountain (10a, 10b, 11a) sees frost end around Rare. This difference matters for onions — but onions handle frost well, so the timing difference is less critical.

Growing Tips

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

Companion Planting

Plant onions alongside these companions for better growth:

Carrots Lettuce Beets Tomatoes

Keep onions away from:

Beans Peas

The Bottom Line

Onions can be grown successfully across Hawaii, but your exact planting dates depend on which region you're in. Coastal Hawaii gardeners should plan around a None last frost, while those in Upcountry/Mountain can typically plant later. For exact dates based on your zip code, use our free planting date finder.

Related Guides

Onions Growing Guide National planting guide with all states Hawaii Planting Calendar All plants for Hawaii Onions in Alabama Alabama planting dates Onions in Alaska Alaska planting dates Onions in Arizona Arizona planting dates Onions in Arkansas Arkansas planting dates
Note: All dates are based on NOAA 30-year Climate Normals and represent historical averages, not predictions for any specific year. Always check your local weather forecast before planting frost-sensitive crops. Learn about our data sources.

Last reviewed: March 29, 2026

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