When to plant cosmos in Spokane, Washington

April 26 – May 10

Transplant outdoors · typical Spokane year

Climate basis: NOAA station Spokane INTL AP, WA (USW00024157), 5 mi (8 km) from downtown Spokane (ZCTA 99201 centroid), elevation 2353 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 26). One year in ten still freezes after May 10.

Last spring freezeApril 261-in-10 after May 10

First fall freezeOctober 121-in-10 before Sep 29

Frost-free season≈ 168 daysmedian at 32°F

Hard freeze, 28°Apr 6 – Oct 23kills even hardy greens

USDA zone7a0 to 5°F winter low — not frost timing

The Spokane year

Transplant outdoorsApr 26 – May 10

Direct-sow outdoorsApr 26 – May 10

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

Cosmos in Spokane · freeze context from Spokane INTL AP, WA, 1991–2020 normals.

Every method, with its sources

Transplant outdoors

Apr 26 – May 10

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 26). NC State Extension · NC State Extension

Direct-sow outdoors

Apr 26 – May 10

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 26). 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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