When to plant cosmos in Syracuse, New York

April 29 – May 13

Transplant outdoors · typical Syracuse year

Climate basis: NOAA station Syracuse Hancock INTL AP, NY (USW00014771), 5 mi (8 km) from downtown Syracuse (ZCTA 13202 centroid), elevation 413 ft, on the 1991–2020 climate normals. Transplant cosmos outdoors from approximately the dates above, anchored to the median last spring 32°F freeze (April 29). One year in ten still freezes after May 13.

Last spring freezeApril 291-in-10 after May 13

First fall freezeOctober 191-in-10 before Oct 2

Frost-free season≈ 173 daysmedian at 32°F

Hard freeze, 28°Apr 16 – Nov 2kills even hardy greens

USDA zone6a-10 to -5°F winter low — not frost timing

The Syracuse year

Transplant outdoorsApr 29 – May 13

Direct-sow outdoorsApr 29 – May 13

indoors under lights
in the garden
frost-free season
1-in-10 years still freeze to May 13

Cosmos in Syracuse · freeze context from Syracuse Hancock INTL AP, NY, 1991–2020 normals.

Every method, with its sources

Transplant outdoors

Apr 29 – May 13

NC Cooperative Extension (Pender County) names cosmos among the large-seeded flowers to transplant outdoors after the threat of frost, giving a two-week set-out window from the last-frost date. Anchored to the median last spring freeze (Apr 29). NC State Extension · NC State Extension

Direct-sow outdoors

Apr 29 – May 13

The NC State Extension Gardener Plant Toolbox (both C. bipinnatus and C. sulphureus entries) and Utah State University Extension agree that cosmos seed goes into the ground once all danger of frost has passed, giving a two-week window from the last-frost date; the accompanying 65F soil requirement is not frost-anchored and was not encoded. Anchored to the median last spring freeze (Apr 29). NC State Extension · NC State Extension · Utah State University Extension

Variety assumption: Covers both common annual garden species (C. bipinnatus and C. sulphureus); no indoor_start rule is encoded because no extension page was found that states a frost-relative indoor-sowing offset for cosmos - Pender County's indoor date is a fixed North Carolina calendar date (mid-March), which the frost-anchored engine cannot honestly express.

These windows describe typical years (1991–2020 climate normals), not this year's forecast. Freezes happen outside them — especially in frost pockets, valleys, and urban edges. Watch the forecast before committing tender plants.

This week, not a typical year:

Crop rule sources (3)

NC State Extension: Cosmos bipinnatus (Cut Leaf Cosmos, Garden Cosmos, Mexican Aster, Tall Cosmos) | North Carolina Extension Gardener Plant Toolbox (accessed 2026-07-25)
"Sow the seeds outdoors after the danger of frost is past and when the soil has warmed to at least 65 degrees."
NC State Extension: Cosmos sulphureus (Klondike Cosmos, Orange Cosmos, Sulphur Cosmos, Yellow Cosmos) | North Carolina Extension Gardener Plant Toolbox (accessed 2026-07-25)
"Sow the seeds outdoors after the danger of frost is past and when the soil has warmed to at least 65 degrees."
Utah State University Extension: Cosmos in the Garden (accessed 2026-07-25)
"Grow plants from seed sown directly into the soil once all danger of frost has passed."

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