When to plant zucchini in St. Louis

Where are you growing?

Comfortable

Not realistic in greenhouse

Comfortable in a cold frame

Zucchini in St. Louis is a good fit outdoors. The suitable growing window of 140 days covers the 45–60 days this plant usually needs.

When to plantMay 11 – July 5

Harvest: June 25 – September 3
Season vs crop: 140 grow days vs 45–60 needed
Typical frost (last spring – first fall): April 18 – November 2

Zucchini in St. Louis is a good fit outdoors. The suitable growing window of 140 days covers the 45–60 days this plant usually needs.

Planting conditions

Direct sow
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 row140

Days to harvest45–60 days from seed

May 11 – Jul 5

Direct sow

Jun 25 – Sep 3

Harvest

Activity	Window	Notes
Direct sow	May 11 – Jul 5	Plant outdoors in this window.
Harvest	Jun 25 – Sep 3	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 – 90 °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

Outdoor sow dateMay 11

Direct sow windowMay 11 – July 5

Suitable growing windowMay 11 – September 27 (140 days)

Expected harvestJune 25 – September 3

How these dates are judged

Ideal conditions: Daytime air from 70 – 90 °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: 45–60 days from seed, 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 Zucchini: May 11 – Sep 27 (140 days)

Planting window for Zucchini: May 11 – Jul 5 (56 days)

Usually too cold: Jan 1 – May 10; 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 20 · May 11 – May 17

Average 58 to 76 °F · Possible 39 to 91 °F

Growing: suitable

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 90 °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 Zucchini 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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