When to plant spinach in Billings, Montana

March 29 – April 19

Transplant outdoors · typical Billings year

Climate basis: NOAA station Billings Wtp, MT (USC00240802), 13 mi (21 km) from downtown Billings (ZCTA 59101 centroid), elevation 3097 ft, on the 1991–2020 climate normals. Transplant spinach outdoors from approximately the dates above, anchored to the median last spring 32°F freeze (May 10). One year in ten still freezes after May 24.

Last spring freezeMay 101-in-10 after May 24

First fall freezeOctober 11-in-10 before Sep 19

Frost-free season≈ 142 daysmedian at 32°F

Hard freeze, 28°Apr 27 – Oct 12kills even hardy greens

USDA zone5a-20 to -15°F winter low — not frost timing

The Billings year

Transplant outdoorsMar 29 – Apr 19

Direct-sow outdoorsApr 10 – Apr 24

Fall plantingAug 6 – Sep 3

indoors under lights
in the garden
frost-free season
1-in-10 years still freeze to May 24

Spinach in Billings · freeze context from Billings Wtp, MT, 1991–2020 normals.

Every method, with its sources

Transplant outdoors

Mar 29 – Apr 19

UNH: safe to set out 3–6 weeks before the last frost. Anchored to the median last spring freeze (May 10). University of New Hampshire Extension

Direct-sow outdoors

Apr 10 – Apr 24

Purdue: hardy — 4–6 weeks before the last frost; Penn State's earliest sowing Apr 1 (−30 days) is the later start and is used. Anchored to the median last spring freeze (May 10). Penn State Extension (York County Master Gardeners) · Purdue University Extension

Fall planting

Aug 6 – Sep 3

Purdue Table 2: plant fall spinach at least 4–8 weeks before the first fall frost. Anchored to the median first fall freeze (Oct 1). Purdue University Extension

Variety assumption: Assumes an average savoy/smooth variety (about 40–50 days; Penn State lists 50).

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 (3)

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.
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.
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.

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