When to Plant Cosmos in Kansas
Delicate, daisy-like blooms that dance in the breeze. Cosmos thrive in poor soil and practically grow themselves.
The Short Answer
Kansas Frost Dates
Your planting dates depend on which part of Kansas you're in. Here are the frost date ranges by region:
| Region | Zones | Last Frost (Spring) | First Frost (Fall) |
|---|---|---|---|
| Northern Kansas | 5b, 6a | Apr 20 - May 5 | Oct 1 - Oct 15 |
| Central Kansas | 6a, 6b | Apr 10 - Apr 25 | Oct 10 - Oct 25 |
| Southern Kansas | 6b, 7a | Apr 1 - Apr 15 | Oct 15 - Nov 1 |
Cosmos Planting Schedule for Kansas
Northern Kansas (Zones 5b, 6a)
Average last frost: Apr 20 - May 5 · Average first frost: Oct 1 - Oct 15
Central Kansas (Zones 6a, 6b)
Average last frost: Apr 10 - Apr 25 · Average first frost: Oct 10 - Oct 25
Southern Kansas (Zones 6b, 7a)
Average last frost: Apr 1 - Apr 15 · Average first frost: Oct 15 - Nov 1
Growing Cosmos in Kansas
Cosmos in Kansas's Climate
Cosmos are the zero-effort flower. Direct sow from mid-May. No fertilizer, no fussing, no deadheading necessary (though it helps). They grow 3-5 feet tall and self-seed prolifically. Perfect for filling unused garden edges with color and pollinator habitat.
Soil Considerations for Kansas
Prairie soils in east — rich and deep. More alkaline and thinner soils in west. Wind erosion can be an issue. Make sure soil has warmed to at least 60°F before planting cosmos outside.
Kansas Climate & Growing Season
Hot summers with strong winds. Severe thunderstorms and hail risk. Drier in the west. Good growing conditions for heat-loving crops. 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 Kansas: Northern Kansas (5b, 6a) has a last frost around Apr 20 - May 5, while Southern Kansas (6b, 7a) sees frost end around Apr 1 - Apr 15. 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