Annual Flower

When to Plant Cosmos in Delaware

Delicate, daisy-like blooms that dance in the breeze. Cosmos thrive in poor soil and practically grow themselves.

The Short Answer

In Delaware, plant cosmos based on your regional frost dates. Northern Delaware has a last frost around Apr 10 - Apr 25, while Southern Delaware sees frost end around Apr 1 - Apr 15. Moderate climate with maritime influence. Good growing conditions for a wide range of vegetables.

Delaware Frost Dates

Your planting dates depend on which part of Delaware you're in. Here are the frost date ranges by region:

Region Zones Last Frost (Spring) First Frost (Fall)
Northern Delaware 7a Apr 10 - Apr 25 Oct 10 - Oct 25
Southern Delaware 7b Apr 1 - Apr 15 Oct 20 - Nov 5

Cosmos Planting Schedule for Delaware

Northern Delaware (Zones 7a)

Average last frost: Apr 10 - Apr 25 · Average first frost: Oct 10 - Oct 25

Start Seeds Indoors
4 wks before frost
Transplant Outside
1 wks after frost
Direct Sow
1 wks after frost

Southern Delaware (Zones 7b)

Average last frost: Apr 1 - Apr 15 · Average first frost: Oct 20 - Nov 5

Start Seeds Indoors
4 wks before frost
Transplant Outside
1 wks after frost
Direct Sow
1 wks after frost

Growing Cosmos in Delaware

Cosmos in Delaware'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 Delaware

Sandy soils in south, clay loam in north. Generally well-drained. Slightly acidic. Make sure soil has warmed to at least 60°F before planting cosmos outside.

Delaware Climate & Growing Season

Moderate climate with maritime influence. Good growing conditions for a wide range of vegetables. 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 Delaware: Northern Delaware (7a) has a last frost around Apr 10 - Apr 25, while Southern Delaware (7b) 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:

Tomatoes Squash

The Bottom Line

Cosmos can be grown successfully across Delaware, but your exact planting dates depend on which region you're in. Northern Delaware gardeners should plan around a Apr 10 - Apr 25 last frost, while those in Southern Delaware can typically plant earlier. For exact dates based on your zip code, use our free planting date finder.

Related Guides

Cosmos Growing Guide National planting guide with all states Delaware Planting Calendar All plants for Delaware Cosmos in Alabama Alabama planting dates Cosmos in Alaska Alaska planting dates Cosmos in Arizona Arizona planting dates Cosmos in Arkansas Arkansas planting dates
Note: All dates are based on NOAA 30-year Climate Normals and represent historical averages, not predictions for any specific year. Always check your local weather forecast before planting frost-sensitive crops. Learn about our data sources.

Last reviewed: March 29, 2026

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