When to plant onions in Baltimore, Maryland

February 24 – March 10

Transplant outdoors · typical Baltimore year

Climate basis: NOAA station Md Sci Ctr Baltimore, MD (USW00093784), 1 mi (2 km) from downtown Baltimore (ZCTA 21202 centroid), elevation 20 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 24). One year in ten still freezes after April 4.

Last spring freezeMarch 241-in-10 after Apr 4

First fall freezeNovember 211-in-10 before Nov 7

Frost-free season≈ 244 daysmedian at 32°F

Hard freeze, 28°Mar 11 – Dec 5kills even hardy greens

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

The Baltimore year

Start seeds indoorsDec 16 – Dec 30

Transplant outdoorsFeb 24 – Mar 10

indoors under lights
in the garden
frost-free season
1-in-10 years still freeze to Apr 4

Onions in Baltimore · freeze context from Md Sci Ctr Baltimore, MD, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Dec 16 – Dec 30

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 24). University of New Hampshire Extension · University of Minnesota Extension

Transplant outdoors

Feb 24 – Mar 10

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 24). 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.

Keep exploring

This crop, other cities

Related crops in Baltimore

Local overview