When to Plant Cosmos in Utah
Delicate, daisy-like blooms that dance in the breeze. Cosmos thrive in poor soil and practically grow themselves.
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 |
Cosmos 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 Cosmos in Utah
Cosmos in Utah's Climate
Cosmos love your heat and sun. Plant from March and enjoy blooms for 6+ months. They handle drought well — one of the most water-efficient flowers for warm-climate gardens. Let some flowers go to seed for naturalized volunteer displays in subsequent years.
Soil Considerations for Utah
Alkaline desert soils. Low organic matter. Saline soils in some areas. Heavy amendment with compost and sulfur needed. Make sure soil has warmed to at least 60°F before planting cosmos outside.
Utah Climate & Growing Season
Arid climate. Intense sun. Low humidity. Wide temperature swings. Irrigation essential everywhere. Cosmos cannot tolerate any frost, so wait until all frost danger has passed before transplanting outside. Watch local forecasts carefully in spring.
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 cosmos — transplant timing shifts by several weeks across the state.
Growing Tips
Don't over-fertilize — rich soil produces more leaves and fewer flowers. Let some flowers go to seed for next year's crop.
Companion Planting
Plant cosmos alongside these companions for better growth:
The Bottom Line
Last reviewed: March 29, 2026