When to plant sunflower in Salt Lake City, Utah

March 31 – April 14

Transplant outdoors · typical Salt Lake City year

Climate basis: NOAA station Salt Lake Triad Ctr, UT (USC00427606), 1 mi (2 km) from downtown Salt Lake City (ZCTA 84111 centroid), elevation 4280 ft, on the 1991–2020 climate normals. Transplant sunflower outdoors from approximately the dates above, anchored to the median last spring 32°F freeze (March 31). One year in ten still freezes after April 19.

Last spring freezeMarch 311-in-10 after Apr 19

First fall freezeNovember 81-in-10 before Oct 23

Frost-free season≈ 224 daysmedian at 32°F

Hard freeze, 28°Mar 8 – Nov 18kills even hardy greens

USDA zone7b5 to 10°F winter low — not frost timing

The Salt Lake City year

Start seeds indoorsMar 10 – Mar 17

Transplant outdoorsMar 31 – Apr 14

Direct-sow outdoorsMar 31 – Apr 14

indoors under lights
in the garden
frost-free season
1-in-10 years still freeze to Apr 19

Sunflower in Salt Lake City · freeze context from Salt Lake Triad Ctr, UT, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Mar 10 – Mar 17

Illinois Extension's '2-3 weeks before planting outdoors' is measured from the after-frost outdoor sowing date, which places the indoor window at 21 to 14 days before last frost. Anchored to the median last spring freeze (Mar 31). University of Illinois Extension · NC State Extension · University of Georgia Cooperative Extension · North Carolina Cooperative Extension, Pender County Center

Transplant outdoors

Mar 31 – Apr 14

NC Cooperative Extension (Pender County) names sunflowers among the large-seeded plants 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 (Mar 31). NC State Extension

Direct-sow outdoors

Mar 31 – Apr 14

Illinois Extension and the NC State Extension Gardener Plant Toolbox both direct-seed sunflowers after the last spring frost, giving a two-week window from the last-frost date; UGA's 'several weeks after the last frost' is later but not a number, so it could not be encoded and only argues for a later start within or beyond this window. Anchored to the median last spring freeze (Mar 31). NC State Extension

Variety assumption: Assumes annual garden and cut-flower sunflowers (Helianthus annuus); the indoor window is deliberately short because sunflowers resent root disturbance.

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 (4)

NC State Extension: Helianthus annuus (Common Sunflower) | North Carolina Extension Gardener Plant Toolbox (accessed 2026-07-25)
"This annual is best planted by seed after the last frost in the spring, and harvested before the first frost in the fall."
University of Illinois Extension: How to grow sunflowers at home - A great addition to any garden | Good Growing (accessed 2026-07-25)
"Sunflowers are typically direct-seeded after the danger of frost has passed (early to mid-May). They can also be started indoors, typically 2-3 weeks before planting outdoors, if you want to get a head start."
University of Georgia Cooperative Extension: Growing Sunflowers in the Home Garden (Circular 1121) (accessed 2026-07-25)
"Sunflowers should be planted several weeks after the last frost."
North Carolina Cooperative Extension, Pender County Center: Growing Flowers and Vegetables From Seed (accessed 2026-07-25)
"Large seeded flowers and vegetables are the easiest to grow and include cucumbers, zucchini, squash, melons, cosmos, marigolds, nasturtium, zinnias, and sunflowers. To get a head start on the season, seeds of these varieties can be sown indoors in mid-March to transplant outdoors after the threat of frost."

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