When to plant onions in Charlotte, North Carolina

March 2 – March 16

Transplant outdoors · typical Charlotte year

Climate basis: NOAA station Charlotte Douglas AP, NC (USW00013881), 6 mi (10 km) from downtown Charlotte (ZCTA 28202 centroid), elevation 728 ft, on the 1991–2020 climate normals. Plant onion sets or transplants from approximately the dates above, anchored to the median last spring 32°F freeze (March 30). One year in ten still freezes after April 14.

Last spring freezeMarch 301-in-10 after Apr 14

First fall freezeNovember 31-in-10 before Oct 22

Frost-free season≈ 221 daysmedian at 32°F

Hard freeze, 28°Mar 17 – Nov 14kills even hardy greens

USDA zone8a10 to 15°F winter low — not frost timing

The Charlotte year

Start seeds indoorsDec 22 – Jan 5

Transplant outdoorsMar 2 – Mar 16

indoors under lights
in the garden
frost-free season
1-in-10 years still freeze to Apr 14

Onions in Charlotte · freeze context from Charlotte Douglas AP, NC, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Dec 22 – Jan 5

Sow 8–10 weeks (UNH) to 10–12 weeks (Minnesota) before planting out; derived from the −4-week set-out date using the UNH lead time. Anchored to the median last spring freeze (Mar 30). University of New Hampshire Extension · University of Minnesota Extension

Transplant outdoors

Mar 2 – Mar 16

UNH: set out transplants (or sets) 4 weeks before the last frost; Purdue's hardy class allows 4–6 weeks before. The later UNH point is used, with a 14-day span. Anchored to the median last spring freeze (Mar 30). University of New Hampshire Extension · Purdue University Extension

Variety assumption: Assumes storage-type bulb onions (about 100–115 days from sets; Penn State lists 105).

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)

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 Minnesota Extension: Growing onions (accessed 2026-07-24)
"You can also raise your own transplants by starting seed indoors 10 to 12 weeks before planting outside."
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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