When to plant snapdragon in St. Louis, Missouri
March 4 – March 18
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 snapdragon 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 18Colorado State's seed-starting table lists snapdragon at 8 weeks before the average frost-free date in the 'Indoors' column, the longest lead time of any source found, so indoor sowing opens 8 weeks before the median last freeze and runs a two-week span. Anchored to the median last spring freeze (Apr 1). Colorado State University Extension
Transplant outdoors
Mar 4 – Mar 18Illinois Extension names snapdragon in its hardy-annual list and states those can usually be planted about four weeks before the frost-free date, and NC State agrees hardy annuals go out in spring before the last frost date, so transplanting opens 4 weeks before the median last freeze. Anchored to the median last spring freeze (Apr 1). NC State Extension
Variety assumption: Assumes ordinary bedding and cut-flower strains of Antirrhinum majus grown as an annual; it is a hardy annual that flowers best in cool weather and Colorado State's 8-week indoor lead time reflects its slow start from very fine seed.
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)
- Colorado State University Extension: Growing Annual Plants from Seed (accessed 2026-07-25)"Table 1: Starting times for seeds grown indoors and in cold frames, shown as number of weeks to start seed before average frost-free date."
- NC State Extension: Extension Gardener Handbook, Ch. 10: Herbaceous Ornamentals (accessed 2026-07-25)"Hardy annuals are the most cold-tolerant. They tolerate light frost and some freezing weather without being killed. In most cases, hardy annuals are planted in the fall or in the spring before the last frost date."