When to plant tomato in St. Louis

Where are you growing?

Comfortable

Not realistic in greenhouse

Comfortable in a cold frame

Tomato in St. Louis is a good fit outdoors. The suitable growing window of 146 days covers the 55–90 days this plant usually needs.

Start indoors: March 6 – April 28
Transplant outside: May 5 – June 27
Harvest: June 29 – September 25
Season vs crop: 146 grow days vs 55–90 needed
Typical frost (last spring – first fall): April 18 – November 2

Tomato in St. Louis is a good fit outdoors. The suitable growing window of 146 days covers the 55–90 days this plant usually needs.

Planting conditions

Start indoors
Harden off
Transplant outside
Grow outdoors
Harvest

Local activity windows for this place and growing method. Blue fill is usually too cold for this plant. Dashed lines are typical last and first frost.

Suitable growing days in a row146

Days to harvest55–90 days from transplant

Mar 6 – Apr 28

Start indoors

Apr 28 – May 4

Harden off

May 5

Transplant outside

May 6 – Jun 28

Grow outdoors

Jun 29 – Sep 25

Harvest

Activity	Window	Notes
Start indoors	Mar 6 – Apr 28	Sow indoors before the outdoor window.
Harden off	Apr 28 – May 4	Acclimate seedlings outdoors before planting.
Transplant outside	May 5	Move plants outside on this day (start of the plant-out window).
Grow outdoors	May 6 – Jun 28	Plants grow outdoors until harvest.
Harvest	Jun 29 – Sep 25	Expected harvest from typical days to harvest.

Blue fill is usually too cold for this plant. Dashed lines are typical last and first frost. Adjust a week or two for your conditions.

Planting and growing across the year

Planting is the sow / plant-out window. Growing is daytime air versus this plant’s ideal (70 – 84 °F) and tolerable (55 – 95 °F) ranges.

Planting uses sow / plant-out rules (frost, soil germination, night, and last-sow): green when plantable, blue diagonal when nights or soil are too cold, amber cross-hatch when too hot, faint for other calendar limits. Growing shows daytime air against this plant’s ideal and tolerable ranges across the year.

Key dates

Typical last spring frostApril 18

Safer last spring frostApril 18

Typical first fall frostNovember 2

Safer first fall frostNovember 2

Frost-free days197

Earliest indoor seed startMarch 6

Latest indoor seed startApril 28

Transplant outdoorsMay 5 – June 27

Direct sow windownot recommended here

Suitable growing windowMay 5 – September 27 (146 days)

Expected harvestJune 29 – September 25

How these dates are judged

Ideal conditions: Daytime air from 70 – 84 °F.
Suitable conditions: Daytime air from 55 – 95 °F.
Last frost and first frost: Typical spring and fall frost dates for St. Louis, shown in the key dates.
Days to harvest: 55–90 days from transplant, from typical days to harvest.
Sowing window: Dated sow and harvest bars use frost dates, soil minima, night limits, and last-sow count-back from typical crop timing. The year strip and weekly chart use the same window: air ratings only colour weeks inside it.

Growing window for Tomato: May 5 – Sep 27 (146 days)

Planting window for Tomato: May 5 – Jun 27 (54 days)

Usually too cold: Jan 1 – May 3; Oct 12 – Dec 31

Outdoors: weekly temperatures and windows

Temperatures across the year for St. Louis. Shaded bands are this plant’s ideal and tolerable daytime air ranges. Growing is daytime air suitability; Planting is sow / plant-out conditions (same colour language). Window brackets mark each stretch.

Ideal range
Tolerable range
Possible min to max
Average min to max
Suitable
Tolerable
Too cold
Too hot

Selected week · tap a week or use the arrows

Week 19 · May 4 – May 10

Average 53 to 71 °F · Possible 40 to 85 °F

Growing: too cold (inside window)

Planting: suitable

A week is in range when its average low and high sit inside the tolerance band 55 to 95 °F; it is suitable when that average range also overlaps the ideal 70 to 84 °F band and possible readings stay within 32 °F to 95 °F. Crossing a possible limit, or missing the ideal band, makes it tolerable; any chance of frost (possible low below 32 °F) makes it too cold. When a sowing window is calculated, weeks outside that window are uncoloured even if air is in range.

Based on average frost dates.

Show all 53 weeks

Cover method weekly charts

Outdoor weekly chart is above. Open a cover chart only if you grow under fleece, a cold frame, or an unheated greenhouse.

Other plants for St. Louis

Calculated by Plan & Plant · Method · Data 2019–2026

Frost and suitability dates are typical figures from climate statistics. Microclimates vary; they are not a guarantee.

How we calculated this

Data: ERA5-Land via Open-Meteo, cell 38.63, -90.20, years 2019–2026 (not a 30-year climate normal yet).
Typical and safer dates: Typical last frost is the date after which half of winters in this sample had no more frost; safer is later in the sample so fewer winters still frosted.
Crop rule: Local windows for Tomato from frost dates, temperature ratings, and crop timing rules.
Confidence: Provisional — short or thin sample for this place.
Full methodology (algorithm 2026-10-season-6).

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