When to plant leeks in Billings, Montana

April 12 – April 26

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 leeks 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

Start seeds indoorsFeb 1 – Feb 15

Transplant outdoorsApr 12 – Apr 26

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

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

Every method, with its sources

Start seeds indoors

Feb 1 – Feb 15

Sow 8–10 weeks before the set-out window opens (UNH: time from seed to transplant 8–10 weeks). Anchored to the median last spring freeze (May 10). University of New Hampshire Extension

Transplant outdoors

Apr 12 – Apr 26

UNH: safe to set out 4 weeks before the last frost; Purdue's hardy class allows 4–6 weeks before. The later UNH start is used. Anchored to the median last spring freeze (May 10). University of New Hampshire Extension · Purdue University Extension

Direct-sow outdoors

Not calculated

Leeks are typically transplanted (Purdue marks leek 'typically transplanted'); the cited guides do not time direct sowing.

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 (2)

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.
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.

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