When to Plant Tomatoes in St. Louis

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GardenSays

Start tomato seeds indoors Feb 13 – Feb 27, transplant outside Apr 17 – Apr 24.

Start seeds indoors: Feb 13 – Feb 27
Transplant outside: Apr 17 – Apr 24
Last frost (typ.): Apr 10

In St. Louis, MO, the typical last frost lands around Apr 10. Working back 6-8 weeks gives you a seed-starting window of Feb 13 – Feb 27 indoors. Tomatoes are killed by frost, so wait until Apr 17-Apr 24 — after frost danger AND once soil hits ~60°F.

That leaves roughly 189 days of growing season before the typical first fall frost (Oct 30) — enough for most varieties. In a short-season area, favor early-maturing varieties (check the days-to-maturity on the tag).

⚠ This year's transplant window (Apr 17 – Apr 24) has passed — dates shown are for planning next season.

Why

✓Frost kills tender seedlings outright, and cold soil stunts them even without frost — both dates matter.
✓The 50% frost date is a planning midpoint: a late frost is still possible, so keep covers handy for the first two weeks.

When this doesn't apply

→Season extenders (row covers, walls of water, cold frames) let you plant 2-3 weeks earlier than these windows.
→Frost dates are area averages — low spots and valley floors run colder than the local average.

How this was calculated

1. Last spring frostApr 10
St. Louis, MO: typical (50% probability) last 32°F frost
2. Seed starting windowFeb 13 – Feb 27
Tomato: start indoors 6-8 weeks before the last frost (Apr 10)
3. Transplant windowApr 17 – Apr 24
Tomato is frost-tender: go out 7-14 days after the last frost, once soil reaches 60°F
4. First fall frostOct 30
St. Louis, MO: typical first 32°F frost in fall — the season's endpoint

Data sources

University of Minnesota Extension — Growing tomatoes in home gardens — Start tomato seeds indoors about 6 weeks before the last frost; transplant after all danger of frost, once soil has warmed. (checked 2026-07-15)
NOAA NCEI — 1991-2020 U.S. Climate Normals (freeze date probabilities) (checked 2026-07-15)
National Gardening Association — frost date lookup (checked 2026-07-15)

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