When to Plant Cosmos in Minnesota
Delicate, daisy-like blooms that dance in the breeze. Cosmos thrive in poor soil and practically grow themselves.
The Short Answer
Minnesota Frost Dates
Your planting dates depend on which part of Minnesota you're in. Here are the frost date ranges by region:
| Region | Zones | Last Frost (Spring) | First Frost (Fall) |
|---|---|---|---|
| Northern Minnesota | 3a, 3b | May 15 - Jun 1 | Sep 5 - Sep 20 |
| Central Minnesota | 3b, 4a | May 5 - May 20 | Sep 15 - Oct 1 |
| Southern Minnesota | 4a, 4b | Apr 25 - May 10 | Sep 25 - Oct 10 |
Cosmos Planting Schedule for Minnesota
Northern Minnesota (Zones 3a, 3b)
Average last frost: May 15 - Jun 1 · Average first frost: Sep 5 - Sep 20
Central Minnesota (Zones 3b, 4a)
Average last frost: May 5 - May 20 · Average first frost: Sep 15 - Oct 1
Southern Minnesota (Zones 4a, 4b)
Average last frost: Apr 25 - May 10 · Average first frost: Sep 25 - Oct 10
Growing Cosmos in Minnesota
Cosmos in Minnesota's Climate
Cosmos bloom reliably even in short-season gardens — direct sow after last frost and enjoy graceful flowers from July through hard frost. They actually prefer poor soil and minimal water, making them one of the lowest-maintenance flowers in any climate. Self-seed for volunteer plants next year.
Soil Considerations for Minnesota
Rich prairie soils in south and west. Rocky and thin soils in north. Generally excellent for gardening in southern half. Make sure soil has warmed to at least 60°F before planting cosmos outside.
Minnesota Climate & Growing Season
Long, cold winters. Warm summers. Short but productive growing season with long summer days. Hardy varieties essential. 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 Minnesota: Northern Minnesota (3a, 3b) has a last frost around May 15 - Jun 1, while Southern Minnesota (4a, 4b) sees frost end around Apr 25 - May 10. 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