Vermont planting calendar

When to plant onions in Vermont — sow, transplant & harvest dates

Vermont is mostly USDA zone 4b (range 3b-5b). Dates below are derived from onions's frost tolerance and Vermont's frost window — not generic national averages.

Onions planting timetable for Vermont

Stage	When in Vermont	Anchor
Start seeds indoors	early March (March 6)	10 weeks before the last frost (mid-May)
Transplant outside	mid-April (April 17)	28 days before the last frost (mid-May)
First harvest (estimate)	early August (August 5)	~110 days from transplant

Dates are state-wide averages for the dominant zone. Local microclimates — elevation, urban heat, coastal moderation — can shift the window by 1-2 weeks. Use the frost-date calculator for a date tuned to your town.

Why Vermont's climate shifts the onions dates

Vermont's last spring frost averages mid-May and first fall frost late September, which sets the whole planting clock. Vermont is a cold, short-season state. The Champlain Valley is the mildest pocket; the mountains and Northeast Kingdom are markedly colder. Sow early — onions bolt once daytime temperatures hold above 24 °C, so the earlier they go in, the longer the harvest.

Onions are day-length sensitive: long-day varieties (zones 1–6) begin bulbing when days exceed 14 hours, short-day types (zones 7–10) bulb at 10–12 hours, and intermediate-day varieties span zones 5–6. Start seeds indoors 10–12 weeks before the last spring frost and transplant out 4–6 weeks before it — young onion seedlings tolerate frost down to about -6 °C once hardened off. In zones 8–10 a second planting from sets in autumn is common, overwintering for an early-summer harvest.

Frost-risk note

Don't plant before mid-May — a hard freeze can still set young plants back. In the Green Mountains and Northeast Kingdom (zone 3b) the safe date runs a week or two later.

Regional variation within Vermont

the Green Mountains and Northeast Kingdom (zone 3b) runs roughly 1-2 weeks behind the state average; the Champlain Valley and southern river valleys (zone 5b) can plant 1-2 weeks earlier.

Burlington — USDA zone 5a
Montpelier — USDA zone 4b
Rutland — USDA zone 5a
Brattleboro — USDA zone 5b

What else to plant in Vermont around then

The same early window suits peas, lettuce, spinach, and onion sets.

Quick-grow guide

Sun: Full sun — 6+ hours direct.
Soil temperature for germination: 10-35 °C (50-95 °F).
Spacing: 4-6 inches (10-15 cm) between plants.
Days to harvest: ~110 days from planting out.

Frequently asked questions

When is the best time to plant onions in Vermont?

In Vermont (mostly USDA zone 4b), sow onions indoors around early March, transplant outdoors mid-April (before the last frost, mid-May), and harvest from early August. Onions are cold-hardy — they tolerate frost and actively prefer cool weather, so they go in well before the last spring frost and bolt in summer heat.

What USDA zone is Vermont?

Most of Vermont sits in USDA hardiness zone 4b, with the state spanning roughly 3b-5b from the Green Mountains and Northeast Kingdom (zone 3b) to the Champlain Valley and southern river valleys (zone 5b). The last spring frost averages mid-May and the first fall frost late September.

Can you grow onions in Vermont?

Yes. Vermont's dominant zone 4b supports onions — the key is timing. Onions are cold-hardy — they tolerate frost and actively prefer cool weather, so they go in well before the last spring frost and bolt in summer heat.

Does the planting date change across Vermont?

the Green Mountains and Northeast Kingdom (zone 3b) runs roughly 1-2 weeks behind the state average; the Champlain Valley and southern river valleys (zone 5b) can plant 1-2 weeks earlier.

What else can I plant in Vermont around the same time?

The same early window suits peas, lettuce, spinach, and onion sets.

Source and methodology

State zone spans from the USDA Plant Hardiness Zone Map (2023); frost-date averages from NOAA Climate Data Online. Hot-state two-season timing cross-checked against the UF/IFAS Florida Gardening Calendar and the University of Arizona Cooperative Extension planting calendar. Curated by the Growli editorial team.