When to plant sweet marjoram in Seattle, Washington

March 13 – March 27

Transplant outdoors · typical Seattle year

Climate basis: NOAA station Seattle Boeing Fld, WA (USW00024234), 5 mi (8 km) from downtown Seattle (ZCTA 98104 centroid), elevation 20 ft, on the 1991–2020 climate normals. Transplant sweet marjoram outdoors from approximately the dates above, anchored to the median last spring 32°F freeze (March 13). One year in ten still freezes after April 1.

Last spring freezeMarch 131-in-10 after Apr 1

First fall freezeNovember 171-in-10 before Nov 1

Frost-free season≈ 247 daysmedian at 32°F

Hard freeze, 28°Feb 18 – Dec 2kills even hardy greens

USDA zone9a20 to 25°F winter low — not frost timing

The Seattle year

Start seeds indoorsJan 16 – Jan 30

Transplant outdoorsMar 13 – Mar 27

Direct-sow outdoorsFeb 27 – Mar 13

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

Sweet Marjoram in Seattle · freeze context from Seattle Boeing Fld, WA, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Jan 16 – Jan 30

NC State's Extension Gardener Plant Toolbox starts marjoram seed indoors about 6 to 8 weeks before the last spring frost date, and Clemson HGIC gives the identical 6-to-8-week lead, so the two sources agree. Anchored to the median last spring freeze (Mar 13). NC State Extension, North Carolina Extension Gardener Plant Toolbox · Clemson University Cooperative Extension, Home & Garden Information Center

Transplant outdoors

Mar 13 – Mar 27

Clemson HGIC sets marjoram transplants out after the last killing frost and UMD Extension names marjoram among herbs planted outside after the danger of frost has passed; both agree, so the window opens at the last spring freeze. Anchored to the median last spring freeze (Mar 13). Clemson University Cooperative Extension, Home & Garden Information Center

Direct-sow outdoors

Feb 27 – Mar 13

NC State's Extension Gardener Plant Toolbox gives a point rule — sow seed directly outdoors about two weeks before the last spring frost date — which opens a two-week sowing span ending at the last freeze; note the transplant window for this tender herb is later. Anchored to the median last spring freeze (Mar 13). NC State Extension, North Carolina Extension Gardener Plant Toolbox

Variety assumption: Grown as an annual across most of the US; NC State's plant toolbox treats it as a tender perennial that is replaced each year in cold climates.

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 (2)

NC State Extension, North Carolina Extension Gardener Plant Toolbox: Origanum majorana (Knotted Marjoram, Marjoram, Pot Marjoram, Sweet Marjoram) (accessed 2026-07-25)
"To plant from seed, start seeds indoors about 6 to 8 weeks prior to the last spring frost date."
Clemson University Cooperative Extension, Home & Garden Information Center: Herbs (accessed 2026-07-25)
"Start seed indoors 6 to 8 weeks before planting or set transplants out after the last killing frost."

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