Annual Flower

When to Plant Cosmos in Massachusetts

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

The Short Answer

In Massachusetts, plant cosmos based on your regional frost dates. Western Massachusetts has a last frost around May 1 - May 20, while Coastal/Cape sees frost end around Apr 15 - May 1. Four seasons. Maritime influence moderates coastal areas. Cold winters. Good growing season with adequate moisture.

Massachusetts Frost Dates

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

Region Zones Last Frost (Spring) First Frost (Fall)
Western Massachusetts 5b, 6a May 1 - May 20 Sep 20 - Oct 10
Central Massachusetts 5b, 6a May 1 - May 15 Sep 25 - Oct 10
Coastal/Cape 6b, 7a Apr 15 - May 1 Oct 15 - Nov 1

Cosmos Planting Schedule for Massachusetts

Western Massachusetts (Zones 5b, 6a)

Average last frost: May 1 - May 20 · Average first frost: Sep 20 - Oct 10

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

Central Massachusetts (Zones 5b, 6a)

Average last frost: May 1 - May 15 · Average first frost: Sep 25 - Oct 10

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

Coastal/Cape (Zones 6b, 7a)

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

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

Growing Cosmos in Massachusetts

Cosmos in Massachusetts'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 Massachusetts

Rocky, acidic New England soils. Glacial deposits. Raised beds popular. Amend heavily with compost. Make sure soil has warmed to at least 60°F before planting cosmos outside.

Massachusetts Climate & Growing Season

Four seasons. Maritime influence moderates coastal areas. Cold winters. Good growing season with adequate moisture. 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 Massachusetts: Western Massachusetts (5b, 6a) has a last frost around May 1 - May 20, while Coastal/Cape (6b, 7a) sees frost end around Apr 15 - 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:

Tomatoes Squash

The Bottom Line

Cosmos can be grown successfully across Massachusetts, but your exact planting dates depend on which region you're in. Western Massachusetts gardeners should plan around a May 1 - May 20 last frost, while those in Coastal/Cape 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 Massachusetts Planting Calendar All plants for Massachusetts 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

Ready to Start Planting?

Enter your zip code and pick your plant. We'll tell you exactly when to plant, start seeds, and harvest — based on where you live.

Find Your Planting Dates