When to plant sweet marjoram in St. Louis, Missouri
April 1 – April 15
Transplant outdoors · typical St. Louis yearClimate basis: NOAA station St Louis Sci Ctr, MO (USC00237452), 4 mi (7 km) from downtown St. Louis (ZCTA 63101 centroid), elevation 515 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 1). One year in ten still freezes after April 18.
The St. Louis year
- indoors under lights
- in the garden
- frost-free season
- 1-in-10 years still freeze to Apr 18
Every method, with its sources
Start seeds indoors
Feb 4 – Feb 18NC 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 1). NC State Extension, North Carolina Extension Gardener Plant Toolbox · Clemson University Cooperative Extension, Home & Garden Information Center
Transplant outdoors
Apr 1 – Apr 15Clemson 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 1). Clemson University Cooperative Extension, Home & Garden Information Center
Direct-sow outdoors
Mar 18 – Apr 1NC 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 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.
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."