When to plant sweet marjoram in Detroit, Michigan

April 21 – May 5

Transplant outdoors · typical Detroit year

Climate basis: NOAA station Detroit City AP, MI (USW00014822), 6 mi (9 km) from downtown Detroit (ZCTA 48226 centroid), elevation 626 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 (April 21). One year in ten still freezes after May 6.

Last spring freezeApril 211-in-10 after May 6

First fall freezeOctober 311-in-10 before Oct 17

Frost-free season≈ 190 daysmedian at 32°F

Hard freeze, 28°Apr 8 – Nov 9kills even hardy greens

USDA zone6b-5 to 0°F winter low — not frost timing

The Detroit year

Start seeds indoorsFeb 24 – Mar 10

Transplant outdoorsApr 21 – May 5

Direct-sow outdoorsApr 7 – Apr 21

indoors under lights
in the garden
frost-free season
1-in-10 years still freeze to May 6

Sweet Marjoram in Detroit · freeze context from Detroit City AP, MI, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Feb 24 – Mar 10

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 (Apr 21). NC State Extension, North Carolina Extension Gardener Plant Toolbox · Clemson University Cooperative Extension, Home & Garden Information Center

Transplant outdoors

Apr 21 – May 5

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 (Apr 21). Clemson University Cooperative Extension, Home & Garden Information Center

Direct-sow outdoors

Apr 7 – Apr 21

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 (Apr 21). 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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