When to plant sweet marjoram in Sioux Falls, South Dakota

May 1 – May 15

Transplant outdoors · typical Sioux Falls year

Climate basis: NOAA station Sioux Falls, SD (USW00014944), 2 mi (3 km) from downtown Sioux Falls (ZCTA 57104 centroid), elevation 1430 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 (May 1). One year in ten still freezes after May 14.

Last spring freezeMay 11-in-10 after May 14

First fall freezeOctober 61-in-10 before Sep 23

Frost-free season≈ 157 daysmedian at 32°F

Hard freeze, 28°Apr 22 – Oct 17kills even hardy greens

USDA zone5a-20 to -15°F winter low — not frost timing

The Sioux Falls year

Start seeds indoorsMar 6 – Mar 20

Transplant outdoorsMay 1 – May 15

Direct-sow outdoorsApr 17 – May 1

indoors under lights
in the garden
frost-free season
1-in-10 years still freeze to May 14

Sweet Marjoram in Sioux Falls · freeze context from Sioux Falls, SD, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Mar 6 – Mar 20

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 (May 1). NC State Extension, North Carolina Extension Gardener Plant Toolbox · Clemson University Cooperative Extension, Home & Garden Information Center

Transplant outdoors

May 1 – May 15

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 (May 1). Clemson University Cooperative Extension, Home & Garden Information Center

Direct-sow outdoors

Apr 17 – May 1

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 (May 1). 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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