When to Plant Onions in Utah
The backbone of the kitchen garden. Choose short-day, intermediate, or long-day varieties based on your latitude.
The Short Answer
Utah Frost Dates
Your planting dates depend on which part of Utah you're in. Here are the frost date ranges by region:
| Region | Zones | Last Frost (Spring) | First Frost (Fall) |
|---|---|---|---|
| Wasatch Front (SLC) | 6a, 6b, 7a | Apr 20 - May 10 | Oct 1 - Oct 20 |
| Mountain Regions | 4a, 4b, 5a | May 25 - Jun 15 | Aug 25 - Sep 15 |
| Southern Utah | 6b, 7a, 7b | Apr 10 - May 1 | Oct 10 - Nov 1 |
Onions Planting Schedule for Utah
Wasatch Front (SLC) (Zones 6a, 6b, 7a)
Average last frost: Apr 20 - May 10 · Average first frost: Oct 1 - Oct 20
Mountain Regions (Zones 4a, 4b, 5a)
Average last frost: May 25 - Jun 15 · Average first frost: Aug 25 - Sep 15
Southern Utah (Zones 6b, 7a, 7b)
Average last frost: Apr 10 - May 1 · Average first frost: Oct 10 - Nov 1
Growing Onions in Utah
Onions in Utah's Climate
You straddle the day-length divide. Southern areas need short-day varieties (plant in fall for spring harvest), northern areas can use intermediate-day types. The single most important decision for onion success in your zone is choosing the right day-length type — the wrong one produces scallions instead of bulbs regardless of how well you grow them.
Soil Considerations for Utah
Alkaline desert soils. Low organic matter. Saline soils in some areas. Heavy amendment with compost and sulfur needed. Loose, well-drained soil is especially important for onions since the edible portion grows underground. If your soil is heavy clay, consider raised beds.
Utah Climate & Growing Season
Arid climate. Intense sun. Low humidity. Wide temperature swings. Irrigation essential everywhere. Onions can handle frost well, which is an advantage in Utah's climate. You can push planting dates earlier in spring and extend into fall.
Growing season length varies across Utah: Wasatch Front (SLC) (6a, 6b, 7a) has a last frost around Apr 20 - May 10, while Southern Utah (6b, 7a, 7b) sees frost end around Apr 10 - May 1. 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:
Keep onions away from:
The Bottom Line
Last reviewed: March 29, 2026