When to Plant Cosmos in Hawaii
Delicate, daisy-like blooms that dance in the breeze. Cosmos thrive in poor soil and practically grow themselves.
The Short Answer
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 |
Cosmos Planting Schedule for Hawaii
Coastal Hawaii (Zones 11a, 11b, 12a, 12b, 13a)
Average last frost: None · Average first frost: None
Upcountry/Mountain (Zones 10a, 10b, 11a)
Average last frost: Rare · Average first frost: Rare
Growing Cosmos in Hawaii
Cosmos in Hawaii's Climate
Cosmos grow during the drier months in subtropical zones. Cosmos sulphureus (Bright Lights) handles humidity better than Cosmos bipinnatus (Sensation). Avoid peak summer humidity periods. The flowers are so low-maintenance that they essentially grow as wildflowers in mild climates.
Soil Considerations for Hawaii
Volcanic soils — extremely fertile but can be acidic. Excellent drainage on slopes. Varies dramatically by island and elevation. Make sure soil has warmed to at least 60°F before planting cosmos outside.
Hawaii Climate & Growing Season
Tropical. Year-round growing season at lower elevations. Elevation creates microclimates. Plant warm-season crops anytime. 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 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 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