When to plant bulb fennel in Burlington, Vermont

April 29 – May 13

Direct-sow outdoors · typical Burlington year

Climate basis: NOAA station Burlington INTL AP, VT (USW00014742), 3 mi (5 km) from downtown Burlington (ZCTA 05401 centroid), elevation 330 ft, on the 1991–2020 climate normals. Direct-sow bulb fennel from approximately the dates above, anchored to the median last spring 32°F freeze (April 29). One year in ten still freezes after May 11.

Last spring freezeApril 291-in-10 after May 11

First fall freezeOctober 151-in-10 before Oct 2

Frost-free season≈ 169 daysmedian at 32°F

Hard freeze, 28°Apr 18 – Oct 28kills even hardy greens

USDA zone5b-15 to -10°F winter low — not frost timing

The Burlington year

Start seeds indoorsMar 18 – Apr 1

Direct-sow outdoorsApr 29 – May 13

indoors under lights
in the garden
frost-free season
1-in-10 years still freeze to May 11

Bulb Fennel in Burlington · freeze context from Burlington INTL AP, VT, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Mar 18 – Apr 1

Wisconsin Horticulture (University of Wisconsin-Madison Division of Extension) states "Plants can be started indoors 4 to 6 weeks before the last spring frost," giving a sowing span from six to four weeks ahead of the last frost; no competing extension figure was found, so it is encoded as printed. Anchored to the median last spring freeze (Apr 29). University of Wisconsin-Madison Division of Extension (Wisconsin Horticulture)

Direct-sow outdoors

Apr 29 – May 13

The same Wisconsin Horticulture article says to "Sow seeds about ¼ inch deep after the last frost in spring, or in mid-summer for a fall crop of Florence fennel," and the first clause is a point rule at the last frost that opens a 14-day sowing span; the article's mid-summer alternative is a fixed-calendar rule with no frost relation and so was not encoded. Anchored to the median last spring freeze (Apr 29). University of Wisconsin-Madison Division of Extension (Wisconsin Horticulture)

Variety assumption: Assumes a bulbing Florence type (finocchio) rather than the non-bulbing herb fennel grown for leaf and seed; the cited article covers Foeniculum vulgare generally but names Florence fennel explicitly in its sowing sentence.

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 (1)

University of Wisconsin-Madison Division of Extension (Wisconsin Horticulture): Fennel, Foeniculum vulgare, Susan Mahr (accessed 2026-07-25)
"Plants can be started indoors 4 to 6 weeks before the last spring frost."

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