When to plant summer squash & zucchini in Oklahoma City, Oklahoma

April 18 – May 2

Transplant outdoors · typical Oklahoma City year

Climate basis: NOAA station Oklahoma City Will Rogers AP, OK (USW00013967), 7 mi (12 km) from downtown Oklahoma City (ZCTA 73102 centroid), elevation 1285 ft, on the 1991–2020 climate normals. Transplant summer squash & zucchini outdoors from approximately the dates above, anchored to the median last spring 32°F freeze (April 4). One year in ten still freezes after April 20.

Last spring freezeApril 41-in-10 after Apr 20

First fall freezeNovember 21-in-10 before Oct 21

Frost-free season≈ 213 daysmedian at 32°F

Hard freeze, 28°Mar 21 – Nov 11kills even hardy greens

USDA zone7b5 to 10°F winter low — not frost timing

The Oklahoma City year

Start seeds indoorsMar 21 – Mar 28

Transplant outdoorsApr 18 – May 2

Direct-sow outdoorsApr 18 – May 2

indoors under lights
in the garden
frost-free season
1-in-10 years still freeze to Apr 20

Summer squash & zucchini in Oklahoma City · freeze context from Oklahoma City Will Rogers AP, OK, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Mar 21 – Mar 28

Sow in pots 3–4 weeks before the outdoor window opens (UNH 3–4 weeks; Missouri G6570 3–5 weeks). Anchored to the median last spring freeze (Apr 4). University of New Hampshire Extension · University of Missouri Extension

Transplant outdoors

Apr 18 – May 2

UNH: set out 2 weeks after last frost; Purdue very-tender class agrees. Anchored to the median last spring freeze (Apr 4). University of New Hampshire Extension · Purdue University Extension

Direct-sow outdoors

Apr 18 – May 2

Purdue: very tender — at least two weeks after the average last frost. Penn State earliest sowing May 15 (+14 days) agrees. Anchored to the median last spring freeze (Apr 4). Purdue University Extension · Penn State Extension (York County Master Gardeners)

Variety assumption: Assumes an average zucchini-type variety (about 50–60 days from seed; Penn State lists 60).

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.

This week, not a typical year:

Crop rule sources (4)

University of New Hampshire Extension: Growing Vegetables: When to Plant Your Vegetable Garden [fact sheet] (accessed 2026-07-24)
Per-crop 'time from seed to transplant' and 'safe to set out in garden' relative to last frost.
University of Missouri Extension: Starting Plants Indoors from Seeds (G6570) (accessed 2026-07-24)
Weeks needed to grow vegetable transplants indoors (Table 2).
Purdue University Extension: Indiana Vegetable Planting Calendar (HO-186-W) (accessed 2026-07-24)
Hardiness classes: hardy = plant 4-6 wk before last spring frost; semi-hardy = 2-4 wk before; tender = after average last frost; very tender = at least 2 wk after. Table 2: fall planting at least 4-8 wk before first fall frost.
Penn State Extension (York County Master Gardeners): Vegetable Seed Planting Guide (accessed 2026-07-24)
Earliest/latest sowing dates for a May 1 last-frost / Oct 1 first-frost baseline; offsets derived by date difference from May 1. Also days-to-maturity figures.

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