When to plant kohlrabi in Boise, Idaho

April 19 – May 3

Transplant outdoors · typical Boise year

Climate basis: NOAA station Boise 7 N, ID (USC00101017), 6 mi (9 km) from downtown Boise (ZCTA 83702 centroid), elevation 3885 ft, on the 1991–2020 climate normals. Transplant kohlrabi outdoors from approximately the dates above, anchored to the median last spring 32°F freeze (May 17). One year in ten still freezes after June 10.

Last spring freezeMay 171-in-10 after Jun 10

First fall freezeOctober 121-in-10 before Sep 27

Frost-free season≈ 147 daysmedian at 32°F

Hard freeze, 28°Apr 27 – Oct 24kills even hardy greens

USDA zone7a0 to 5°F winter low — not frost timing

The Boise year

Start seeds indoorsMar 8 – Mar 22

Transplant outdoorsApr 19 – May 3

Fall plantingAug 17 – Sep 14

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

Kohlrabi in Boise · freeze context from Boise 7 N, ID, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Mar 8 – Mar 22

Sow 4–6 weeks before the set-out window opens (UNH: time from seed to transplant 4–6 weeks). Anchored to the median last spring freeze (May 17). University of New Hampshire Extension

Transplant outdoors

Apr 19 – May 3

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 17). University of New Hampshire Extension · Purdue University Extension

Fall planting

Aug 17 – Sep 14

Purdue Table 2: plant fall kohlrabi at least 4–8 weeks before the first fall frost. Anchored to the median first fall freeze (Oct 12). Purdue University Extension

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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